From 1123e684c5a05db4fb15f0f2f8d1d0dc179ff102 Mon Sep 17 00:00:00 2001
From: Justin Grant <justingrant@users.noreply.github.com>
Date: Sun, 15 Aug 2021 20:45:11 -0700
Subject: [PATCH] Replace `'' + obj` pattern with `''.concat(obj)`

Using the `+` operator to concatenate strings and objects is problematic
because `+` calls `valueOf` which will throw for some types.
See #20594 for details.

This commit globally replaces `'' + obj` with `''.concat(obj)`, which
does the same thing but doesn't call `valueOf` before converting to a
string.

It also updates the code example in the lint rule that encouaged use of
this problematic pattern.
---
 .../fixtures/error-handling/index.js          |  2 +-
 .../cjs/react-jsx-dev-runtime.development.js  |  6 +++---
 .../cjs/react-jsx-runtime.development.js      |  6 +++---
 .../cjs/react-jsx-dev-runtime.development.js  |  6 +++---
 .../cjs/react-jsx-runtime.development.js      |  6 +++---
 .../cjs/react-jsx-dev-runtime.development.js  |  6 +++---
 .../cjs/react-jsx-runtime.development.js      |  6 +++---
 .../cjs/react-jsx-dev-runtime.development.js  |  6 +++---
 .../cjs/react-jsx-runtime.development.js      |  6 +++---
 .../react-devtools-extensions/src/main.js     |  2 +-
 .../src/backend/legacy/renderer.js            |  2 +-
 .../src/backend/renderer.js                   |  2 +-
 .../src/backend/utils.js                      |  6 +++---
 .../views/ErrorBoundary/ErrorBoundary.js      |  2 +-
 .../src/devtools/views/utils.js               |  4 ++--
 packages/react-devtools-shared/src/utils.js   |  2 +-
 .../src/__tests__/ReactDOMInput-test.js       |  2 +-
 .../src/__tests__/ReactDOMTextarea-test.js    |  2 +-
 .../src/__tests__/ReactMultiChildText-test.js |  4 ++--
 .../src/client/DOMPropertyOperations.js       | 14 ++++++-------
 .../react-dom/src/client/ReactDOMComponent.js | 10 +++++-----
 .../src/client/ReactDOMHostConfig.js          |  4 ++--
 .../react-dom/src/client/ReactDOMInput.js     |  2 +-
 .../react-dom/src/client/ToStringValue.js     |  2 +-
 .../src/client/inputValueTracking.js          |  6 +++---
 .../src/server/DOMMarkupOperations.js         |  2 +-
 .../src/server/ReactDOMServerFormatConfig.js  | 20 +++++++++----------
 .../src/server/ReactPartialRenderer.js        | 10 +++++-----
 .../src/server/escapeTextForBrowser.js        |  4 ++--
 .../src/shared/dangerousStyleValue.js         |  2 +-
 .../src/test-utils/ReactTestUtils.js          |  2 +-
 .../react-noop-renderer/flight-modules.js     |  2 +-
 .../react-noop-renderer/npm/flight-modules.js |  2 +-
 .../src/createReactNoop.js                    |  4 ++--
 .../src/ReactChildFiber.new.js                | 10 +++++-----
 .../src/ReactChildFiber.old.js                | 10 +++++-----
 packages/react-reconciler/src/ReactPortal.js  |  2 +-
 .../src/__tests__/ReactIncremental-test.js    |  4 ++--
 .../src/__tests__/ReactMemo-test.js           |  2 +-
 .../src/__tests__/ReactPersistent-test.js     |  2 +-
 .../ReactFlightDOMRelayServerHostConfig.js    |  2 +-
 .../src/ReactFlightWebpackPlugin.js           |  2 +-
 .../src/__tests__/ReactFlightDOM-test.js      |  2 +-
 .../ReactFlightNativeRelayServerHostConfig.js |  2 +-
 packages/react-server/src/ReactFizzServer.js  |  2 +-
 .../react-server/src/ReactFlightServer.js     |  6 +++---
 .../src/ReactTestRenderer.js                  |  2 +-
 packages/react/src/ReactChildren.js           |  6 +++---
 packages/react/src/ReactElement.js            | 12 +++++------
 packages/react/src/jsx/ReactJSXElement.js     |  8 ++++----
 packages/shared/consoleWithStackDev.js        |  2 +-
 scripts/error-codes/extract-errors.js         |  2 +-
 ...no-primitive-constructors-test.internal.js |  4 ++--
 .../eslint-rules/no-primitive-constructors.js |  2 +-
 scripts/merge-fork/merge-fork.js              |  4 ++--
 55 files changed, 126 insertions(+), 126 deletions(-)

diff --git a/fixtures/dom/src/components/fixtures/error-handling/index.js b/fixtures/dom/src/components/fixtures/error-handling/index.js
index 5bbeec7de447eb..d0d8627b16d311 100644
--- a/fixtures/dom/src/components/fixtures/error-handling/index.js
+++ b/fixtures/dom/src/components/fixtures/error-handling/index.js
@@ -41,7 +41,7 @@ class ErrorBoundary extends React.Component {
       if (this.state.error) {
         return <p>Captured an error: {this.state.error.message}</p>;
       } else {
-        return <p>Captured an error: {'' + this.state.error}</p>;
+        return <p>Captured an error: {''.concat(this.state.error)}</p>;
       }
     }
     if (this.state.shouldThrow) {
diff --git a/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-dev-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-dev-runtime.development.js
index 31238ef27cf806..be8fe12161d0f8 100644
--- a/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-dev-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-dev-runtime.development.js
@@ -104,7 +104,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -483,11 +483,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-runtime.development.js
index 5658993188aece..92c101038edaf0 100644
--- a/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-14/cjs/react-jsx-runtime.development.js
@@ -103,7 +103,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -487,11 +487,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-dev-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-dev-runtime.development.js
index ecad786788f052..eee05e356f439d 100644
--- a/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-dev-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-dev-runtime.development.js
@@ -109,7 +109,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -488,11 +488,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-runtime.development.js
index 9fce32b1c1e4ca..4c6ce3c86669a7 100644
--- a/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-15/cjs/react-jsx-runtime.development.js
@@ -108,7 +108,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -492,11 +492,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-dev-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-dev-runtime.development.js
index 880e9b652f0ba6..4dc95bb27d7602 100644
--- a/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-dev-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-dev-runtime.development.js
@@ -115,7 +115,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -509,11 +509,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-runtime.development.js
index 76e6f2457b9c4f..e2a031f1108ff9 100644
--- a/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-16/cjs/react-jsx-runtime.development.js
@@ -114,7 +114,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -513,11 +513,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-dev-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-dev-runtime.development.js
index 3b7122293e1bc9..5400ccbf57a655 100644
--- a/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-dev-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-dev-runtime.development.js
@@ -107,7 +107,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -815,11 +815,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-runtime.development.js b/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-runtime.development.js
index 690bebdf52523a..368daed1928eb3 100644
--- a/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-runtime.development.js
+++ b/fixtures/legacy-jsx-runtimes/react-17/cjs/react-jsx-runtime.development.js
@@ -107,7 +107,7 @@ function printWarning(level, format, args) {
     }
 
     var argsWithFormat = args.map(function (item) {
-      return '' + item;
+      return ''.concat(item);
     }); // Careful: RN currently depends on this prefix
 
     argsWithFormat.unshift('Warning: ' + format); // We intentionally don't use spread (or .apply) directly because it
@@ -815,11 +815,11 @@ function jsxDEV(type, config, maybeKey, source, self) {
     // key is explicitly declared to be undefined or not.
 
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/packages/react-devtools-extensions/src/main.js b/packages/react-devtools-extensions/src/main.js
index 514e48514d785c..277f8676561df2 100644
--- a/packages/react-devtools-extensions/src/main.js
+++ b/packages/react-devtools-extensions/src/main.js
@@ -82,7 +82,7 @@ function createPanelIfReactLoaded() {
 
       function initBridgeAndStore() {
         const port = chrome.runtime.connect({
-          name: '' + tabId,
+          name: ''.concat(tabId),
         });
         // Looks like `port.onDisconnect` does not trigger on in-tab navigation like new URL or back/forward navigation,
         // so it makes no sense to handle it here.
diff --git a/packages/react-devtools-shared/src/backend/legacy/renderer.js b/packages/react-devtools-shared/src/backend/legacy/renderer.js
index 7b612ff346171e..01cafdf3bfd07e 100644
--- a/packages/react-devtools-shared/src/backend/legacy/renderer.js
+++ b/packages/react-devtools-shared/src/backend/legacy/renderer.js
@@ -63,7 +63,7 @@ function getData(internalInstance: InternalInstance) {
   // != used deliberately here to catch undefined and null
   if (internalInstance._currentElement != null) {
     if (internalInstance._currentElement.key) {
-      key = '' + internalInstance._currentElement.key;
+      key = ''.concat(internalInstance._currentElement.key);
     }
 
     const elementType = internalInstance._currentElement.type;
diff --git a/packages/react-devtools-shared/src/backend/renderer.js b/packages/react-devtools-shared/src/backend/renderer.js
index 62341ce300ec00..9e407eadda83ec 100644
--- a/packages/react-devtools-shared/src/backend/renderer.js
+++ b/packages/react-devtools-shared/src/backend/renderer.js
@@ -1838,7 +1838,7 @@ export function attach(
 
       // This check is a guard to handle a React element that has been modified
       // in such a way as to bypass the default stringification of the "key" property.
-      const keyString = key === null ? null : '' + key;
+      const keyString = key === null ? null : ''.concat(key);
       const keyStringID = getStringID(keyString);
 
       pushOperation(TREE_OPERATION_ADD);
diff --git a/packages/react-devtools-shared/src/backend/utils.js b/packages/react-devtools-shared/src/backend/utils.js
index 60fabfa03c8931..b852e49c725b7d 100644
--- a/packages/react-devtools-shared/src/backend/utils.js
+++ b/packages/react-devtools-shared/src/backend/utils.js
@@ -169,7 +169,7 @@ export function format(
   let formatted: string =
     typeof maybeMessage === 'symbol'
       ? maybeMessage.toString()
-      : '' + maybeMessage;
+      : ''.concat(maybeMessage);
 
   // If the first argument is a string, check for substitutions.
   if (typeof maybeMessage === 'string') {
@@ -205,14 +205,14 @@ export function format(
       const arg = args[i];
 
       // Symbols cannot be concatenated with Strings.
-      formatted += ' ' + (typeof arg === 'symbol' ? arg.toString() : arg);
+      formatted += ' ' + (typeof arg === 'symbol' ? arg.toString() : ''.concat(arg));
     }
   }
 
   // Update escaped %% values.
   formatted = formatted.replace(/%{2,2}/g, '%');
 
-  return '' + formatted;
+  return ''.concat(formatted);
 }
 
 export function isSynchronousXHRSupported(): boolean {
diff --git a/packages/react-devtools-shared/src/devtools/views/ErrorBoundary/ErrorBoundary.js b/packages/react-devtools-shared/src/devtools/views/ErrorBoundary/ErrorBoundary.js
index c7aa20dcd5902e..ae02af3680fc40 100644
--- a/packages/react-devtools-shared/src/devtools/views/ErrorBoundary/ErrorBoundary.js
+++ b/packages/react-devtools-shared/src/devtools/views/ErrorBoundary/ErrorBoundary.js
@@ -46,7 +46,7 @@ export default class ErrorBoundary extends Component<Props, State> {
       error !== null &&
       error.hasOwnProperty('message')
         ? error.message
-        : '' + error;
+        : ''.concat(error);
 
     const callStack =
       typeof error === 'object' &&
diff --git a/packages/react-devtools-shared/src/devtools/views/utils.js b/packages/react-devtools-shared/src/devtools/views/utils.js
index b326996daa05af..c5460c37a128c5 100644
--- a/packages/react-devtools-shared/src/devtools/views/utils.js
+++ b/packages/react-devtools-shared/src/devtools/views/utils.js
@@ -19,8 +19,8 @@ export function alphaSortEntries(
 ): number {
   const a = entryA[0];
   const b = entryB[0];
-  if ('' + +a === a) {
-    if ('' + +b !== b) {
+  if (''.concat(+a) === a) {
+    if (''.concat(+b) !== b) {
       return -1;
     }
     return +a < +b ? -1 : 1;
diff --git a/packages/react-devtools-shared/src/utils.js b/packages/react-devtools-shared/src/utils.js
index 573679f635ab8f..e2ae9bd20683e2 100644
--- a/packages/react-devtools-shared/src/utils.js
+++ b/packages/react-devtools-shared/src/utils.js
@@ -805,7 +805,7 @@ export function formatDataForPreview(
       return data;
     default:
       try {
-        return truncateForDisplay('' + data);
+        return truncateForDisplay(''.concat(data));
       } catch (error) {
         return 'unserializable';
       }
diff --git a/packages/react-dom/src/__tests__/ReactDOMInput-test.js b/packages/react-dom/src/__tests__/ReactDOMInput-test.js
index 018dd14697f08a..e35831de0225fa 100644
--- a/packages/react-dom/src/__tests__/ReactDOMInput-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMInput-test.js
@@ -1575,7 +1575,7 @@ describe('ReactDOMInput', () => {
             return value;
           },
           set: function(val) {
-            value = '' + val;
+            value = ''.concat(val);
             log.push('set property value');
           },
         });
diff --git a/packages/react-dom/src/__tests__/ReactDOMTextarea-test.js b/packages/react-dom/src/__tests__/ReactDOMTextarea-test.js
index 4d56f53d9e40c6..cd87ebd4881dd2 100644
--- a/packages/react-dom/src/__tests__/ReactDOMTextarea-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMTextarea-test.js
@@ -142,7 +142,7 @@ describe('ReactDOMTextarea', () => {
             return value;
           },
           set: function(val) {
-            value = '' + val;
+            value = ''.concat(val);
             counter++;
           },
         });
diff --git a/packages/react-dom/src/__tests__/ReactMultiChildText-test.js b/packages/react-dom/src/__tests__/ReactMultiChildText-test.js
index 467cbf59c2e067..a8d13d15e7b3f0 100644
--- a/packages/react-dom/src/__tests__/ReactMultiChildText-test.js
+++ b/packages/react-dom/src/__tests__/ReactMultiChildText-test.js
@@ -44,7 +44,7 @@ const expectChildren = function(container, children) {
     } else {
       expect(textNode != null).toBe(true);
       expect(textNode.nodeType).toBe(3);
-      expect(textNode.data).toBe('' + children);
+      expect(textNode.data).toBe(''.concat(children));
     }
   } else {
     let mountIndex = 0;
@@ -55,7 +55,7 @@ const expectChildren = function(container, children) {
       if (typeof child === 'string') {
         textNode = outerNode.childNodes[mountIndex];
         expect(textNode.nodeType).toBe(3);
-        expect(textNode.data).toBe('' + child);
+        expect(textNode.data).toBe(''.concat(child));
         mountIndex++;
       } else {
         const elementDOMNode = outerNode.childNodes[mountIndex];
diff --git a/packages/react-dom/src/client/DOMPropertyOperations.js b/packages/react-dom/src/client/DOMPropertyOperations.js
index 2dcb1ace8ab9f5..9bd3b5f09c7bdf 100644
--- a/packages/react-dom/src/client/DOMPropertyOperations.js
+++ b/packages/react-dom/src/client/DOMPropertyOperations.js
@@ -44,7 +44,7 @@ export function getValueForProperty(
         // If we haven't fully disabled javascript: URLs, and if
         // the hydration is successful of a javascript: URL, we
         // still want to warn on the client.
-        sanitizeURL('' + (expected: any));
+        sanitizeURL(''.concat((expected: any)));
       }
 
       const attributeName = propertyInfo.attributeName;
@@ -60,7 +60,7 @@ export function getValueForProperty(
           if (shouldRemoveAttribute(name, expected, propertyInfo, false)) {
             return value;
           }
-          if (value === '' + (expected: any)) {
+          if (value === ''.concat((expected: any))) {
             return expected;
           }
           return value;
@@ -85,7 +85,7 @@ export function getValueForProperty(
 
       if (shouldRemoveAttribute(name, expected, propertyInfo, false)) {
         return stringValue === null ? expected : stringValue;
-      } else if (stringValue === '' + (expected: any)) {
+      } else if (stringValue === ''.concat((expected: any))) {
         return expected;
       } else {
         return stringValue;
@@ -119,7 +119,7 @@ export function getValueForAttribute(
       return expected === undefined ? undefined : null;
     }
     const value = node.getAttribute(name);
-    if (value === '' + (expected: any)) {
+    if (value === ''.concat((expected: any))) {
       return expected;
     }
     return value;
@@ -155,7 +155,7 @@ export function setValueForProperty(
       } else {
         node.setAttribute(
           attributeName,
-          enableTrustedTypesIntegration ? (value: any) : '' + (value: any),
+          enableTrustedTypesIntegration ? (value: any) : ''.concat((value: any)),
         );
       }
     }
@@ -187,11 +187,11 @@ export function setValueForProperty(
       attributeValue = '';
     } else {
       // `setAttribute` with objects becomes only `[object]` in IE8/9,
-      // ('' + value) makes it output the correct toString()-value.
+      // (''.concat(value)) makes it output the correct toString()-value.
       if (enableTrustedTypesIntegration) {
         attributeValue = (value: any);
       } else {
-        attributeValue = '' + (value: any);
+        attributeValue = ''.concat((value: any));
       }
       if (propertyInfo.sanitizeURL) {
         sanitizeURL(attributeValue.toString());
diff --git a/packages/react-dom/src/client/ReactDOMComponent.js b/packages/react-dom/src/client/ReactDOMComponent.js
index 7820978957107c..16f8abd7cd3f7d 100644
--- a/packages/react-dom/src/client/ReactDOMComponent.js
+++ b/packages/react-dom/src/client/ReactDOMComponent.js
@@ -140,7 +140,7 @@ if (__DEV__) {
 
   normalizeMarkupForTextOrAttribute = function(markup: mixed): string {
     const markupString =
-      typeof markup === 'string' ? markup : '' + (markup: any);
+      typeof markup === 'string' ? markup : ''.concat((markup: any));
     return markupString
       .replace(NORMALIZE_NEWLINES_REGEX, '\n')
       .replace(NORMALIZE_NULL_AND_REPLACEMENT_REGEX, '');
@@ -303,7 +303,7 @@ function setInitialDOMProperties(
           setTextContent(domElement, nextProp);
         }
       } else if (typeof nextProp === 'number') {
-        setTextContent(domElement, '' + nextProp);
+        setTextContent(domElement, ''.concat(nextProp));
       }
     } else if (
       propKey === SUPPRESS_CONTENT_EDITABLE_WARNING ||
@@ -748,7 +748,7 @@ export function diffProperties(
       }
     } else if (propKey === CHILDREN) {
       if (typeof nextProp === 'string' || typeof nextProp === 'number') {
-        (updatePayload = updatePayload || []).push(propKey, '' + nextProp);
+        (updatePayload = updatePayload || []).push(propKey, ''.concat(nextProp));
       }
     } else if (
       propKey === SUPPRESS_CONTENT_EDITABLE_WARNING ||
@@ -981,11 +981,11 @@ export function diffHydratedProperties(
           updatePayload = [CHILDREN, nextProp];
         }
       } else if (typeof nextProp === 'number') {
-        if (domElement.textContent !== '' + nextProp) {
+        if (domElement.textContent !== ''.concat(nextProp)) {
           if (__DEV__ && !suppressHydrationWarning) {
             warnForTextDifference(domElement.textContent, nextProp);
           }
-          updatePayload = [CHILDREN, '' + nextProp];
+          updatePayload = [CHILDREN, ''.concat(nextProp)];
         }
       }
     } else if (registrationNameDependencies.hasOwnProperty(propKey)) {
diff --git a/packages/react-dom/src/client/ReactDOMHostConfig.js b/packages/react-dom/src/client/ReactDOMHostConfig.js
index 74877c1591e756..5457938ee68ba7 100644
--- a/packages/react-dom/src/client/ReactDOMHostConfig.js
+++ b/packages/react-dom/src/client/ReactDOMHostConfig.js
@@ -275,7 +275,7 @@ export function createInstance(
       typeof props.children === 'string' ||
       typeof props.children === 'number'
     ) {
-      const string = '' + props.children;
+      const string = ''.concat(props.children);
       const ownAncestorInfo = updatedAncestorInfo(
         hostContextDev.ancestorInfo,
         type,
@@ -330,7 +330,7 @@ export function prepareUpdate(
       (typeof newProps.children === 'string' ||
         typeof newProps.children === 'number')
     ) {
-      const string = '' + newProps.children;
+      const string = ''.concat(newProps.children);
       const ownAncestorInfo = updatedAncestorInfo(
         hostContextDev.ancestorInfo,
         type,
diff --git a/packages/react-dom/src/client/ReactDOMInput.js b/packages/react-dom/src/client/ReactDOMInput.js
index c1afd277e3e930..c32682f0cd4cfe 100644
--- a/packages/react-dom/src/client/ReactDOMInput.js
+++ b/packages/react-dom/src/client/ReactDOMInput.js
@@ -366,7 +366,7 @@ function updateNamedCousins(rootNode, props) {
     // document. Let's just use the local `querySelectorAll` to ensure we don't
     // miss anything.
     const group = queryRoot.querySelectorAll(
-      'input[name=' + JSON.stringify('' + name) + '][type="radio"]',
+      'input[name=' + JSON.stringify(''.concat(name)) + '][type="radio"]',
     );
 
     for (let i = 0; i < group.length; i++) {
diff --git a/packages/react-dom/src/client/ToStringValue.js b/packages/react-dom/src/client/ToStringValue.js
index 41826cd404e05f..7c77adbf9b599e 100644
--- a/packages/react-dom/src/client/ToStringValue.js
+++ b/packages/react-dom/src/client/ToStringValue.js
@@ -19,7 +19,7 @@ export opaque type ToStringValue =
 // around this limitation, we use an opaque type that can only be obtained by
 // passing the value through getToStringValue first.
 export function toString(value: ToStringValue): string {
-  return '' + (value: any);
+  return ''.concat((value: any));
 }
 
 export function getToStringValue(value: mixed): ToStringValue {
diff --git a/packages/react-dom/src/client/inputValueTracking.js b/packages/react-dom/src/client/inputValueTracking.js
index 54c850662ab2b5..f174d481d80311 100644
--- a/packages/react-dom/src/client/inputValueTracking.js
+++ b/packages/react-dom/src/client/inputValueTracking.js
@@ -55,7 +55,7 @@ function trackValueOnNode(node: any): ?ValueTracker {
     valueField,
   );
 
-  let currentValue = '' + node[valueField];
+  let currentValue = ''.concat(node[valueField]);
 
   // if someone has already defined a value or Safari, then bail
   // and don't track value will cause over reporting of changes,
@@ -76,7 +76,7 @@ function trackValueOnNode(node: any): ?ValueTracker {
       return get.call(this);
     },
     set: function(value) {
-      currentValue = '' + value;
+      currentValue = ''.concat(value);
       set.call(this, value);
     },
   });
@@ -93,7 +93,7 @@ function trackValueOnNode(node: any): ?ValueTracker {
       return currentValue;
     },
     setValue(value) {
-      currentValue = '' + value;
+      currentValue = ''.concat(value);
     },
     stopTracking() {
       detachTracker(node);
diff --git a/packages/react-dom/src/server/DOMMarkupOperations.js b/packages/react-dom/src/server/DOMMarkupOperations.js
index 014e6355319266..8b12b5257d7bde 100644
--- a/packages/react-dom/src/server/DOMMarkupOperations.js
+++ b/packages/react-dom/src/server/DOMMarkupOperations.js
@@ -44,7 +44,7 @@ export function createMarkupForProperty(name: string, value: mixed): string {
       return attributeName + '=""';
     } else {
       if (propertyInfo.sanitizeURL) {
-        value = '' + (value: any);
+        value = ''.concat((value: any));
         sanitizeURL(value);
       }
       return attributeName + '=' + quoteAttributeValueForBrowser(value);
diff --git a/packages/react-dom/src/server/ReactDOMServerFormatConfig.js b/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
index 9232106aac362d..2bef2e355a2378 100644
--- a/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
+++ b/packages/react-dom/src/server/ReactDOMServerFormatConfig.js
@@ -310,7 +310,7 @@ function pushStyle(
     if (isCustomProperty) {
       nameChunk = stringToChunk(escapeTextForBrowser(styleName));
       valueChunk = stringToChunk(
-        escapeTextForBrowser(('' + styleValue).trim()),
+        escapeTextForBrowser((''.concat(styleValue)).trim()),
       );
     } else {
       if (__DEV__) {
@@ -325,11 +325,11 @@ function pushStyle(
         ) {
           valueChunk = stringToChunk(styleValue + 'px'); // Presumes implicit 'px' suffix for unitless numbers
         } else {
-          valueChunk = stringToChunk('' + styleValue);
+          valueChunk = stringToChunk(''.concat(styleValue));
         }
       } else {
         valueChunk = stringToChunk(
-          escapeTextForBrowser(('' + styleValue).trim()),
+          escapeTextForBrowser((''.concat(styleValue)).trim()),
         );
       }
     }
@@ -476,7 +476,7 @@ function pushAttribute(
         break;
       default:
         if (propertyInfo.sanitizeURL) {
-          value = '' + (value: any);
+          value = ''.concat((value: any));
           sanitizeURL(value);
         }
         target.push(
@@ -557,7 +557,7 @@ function pushInnerHTML(
     );
     const html = innerHTML.__html;
     if (html !== null && html !== undefined) {
-      target.push(stringToChunk('' + html));
+      target.push(stringToChunk(''.concat(html)));
     }
   }
 }
@@ -745,7 +745,7 @@ function pushStartOption(
   if (selectedValue !== null) {
     let stringValue;
     if (value !== null) {
-      stringValue = '' + value;
+      stringValue = ''.concat(value);
     } else {
       if (__DEV__) {
         if (innerHTML !== null) {
@@ -763,7 +763,7 @@ function pushStartOption(
     if (isArray(selectedValue)) {
       // multiple
       for (let i = 0; i < selectedValue.length; i++) {
-        const v = '' + selectedValue[i];
+        const v = ''.concat(selectedValue[i]);
         if (v === stringValue) {
           target.push(selectedMarkerAttribute);
           break;
@@ -975,9 +975,9 @@ function pushStartTextArea(
         children.length <= 1,
         '<textarea> can only have at most one child.',
       );
-      value = '' + children[0];
+      value = ''.concat(children[0]);
     }
-    value = '' + children;
+    value = ''.concat(children);
   }
 
   if (typeof value === 'string' && value[0] === '\n') {
@@ -1242,7 +1242,7 @@ function pushStartPreformattedElement(
       if (typeof html === 'string' && html.length > 0 && html[0] === '\n') {
         target.push(leadingNewline, stringToChunk(html));
       } else {
-        target.push(stringToChunk('' + html));
+        target.push(stringToChunk(''.concat(html)));
       }
     }
   }
diff --git a/packages/react-dom/src/server/ReactPartialRenderer.js b/packages/react-dom/src/server/ReactPartialRenderer.js
index caf1ee2f6fc294..e1a6ebffcc8d1c 100644
--- a/packages/react-dom/src/server/ReactPartialRenderer.js
+++ b/packages/react-dom/src/server/ReactPartialRenderer.js
@@ -1010,7 +1010,7 @@ class ReactDOMServerRenderer {
     parentNamespace: string,
   ): string {
     if (typeof child === 'string' || typeof child === 'number') {
-      const text = '' + child;
+      const text = ''.concat(child);
       if (text === '') {
         return '';
       }
@@ -1472,7 +1472,7 @@ class ReactDOMServerRenderer {
             textareaChildren = textareaChildren[0];
           }
 
-          defaultValue = '' + textareaChildren;
+          defaultValue = ''.concat(textareaChildren);
         }
         if (defaultValue == null) {
           defaultValue = '';
@@ -1482,7 +1482,7 @@ class ReactDOMServerRenderer {
 
       props = Object.assign({}, props, {
         value: undefined,
-        children: '' + initialValue,
+        children: ''.concat(initialValue),
       });
     } else if (tag === 'select') {
       if (__DEV__) {
@@ -1554,13 +1554,13 @@ class ReactDOMServerRenderer {
         if (isArray(selectValue)) {
           // multiple
           for (let j = 0; j < selectValue.length; j++) {
-            if ('' + selectValue[j] === value) {
+            if (''.concat(selectValue[j]) === value) {
               selected = true;
               break;
             }
           }
         } else {
-          selected = '' + selectValue === value;
+          selected = ''.concat(selectValue) === value;
         }
 
         props = Object.assign(
diff --git a/packages/react-dom/src/server/escapeTextForBrowser.js b/packages/react-dom/src/server/escapeTextForBrowser.js
index 2a5a91aafde3c5..e7e4183c2ae505 100644
--- a/packages/react-dom/src/server/escapeTextForBrowser.js
+++ b/packages/react-dom/src/server/escapeTextForBrowser.js
@@ -47,7 +47,7 @@ const matchHtmlRegExp = /["'&<>]/;
  */
 
 function escapeHtml(string) {
-  const str = '' + string;
+  const str = ''.concat(string);
   const match = matchHtmlRegExp.exec(str);
 
   if (!match) {
@@ -103,7 +103,7 @@ function escapeTextForBrowser(text) {
     // this shortcircuit helps perf for types that we know will never have
     // special characters, especially given that this function is used often
     // for numeric dom ids.
-    return '' + text;
+    return ''.concat(text);
   }
   return escapeHtml(text);
 }
diff --git a/packages/react-dom/src/shared/dangerousStyleValue.js b/packages/react-dom/src/shared/dangerousStyleValue.js
index 53d32e9126d668..bb73b7d3930118 100644
--- a/packages/react-dom/src/shared/dangerousStyleValue.js
+++ b/packages/react-dom/src/shared/dangerousStyleValue.js
@@ -41,7 +41,7 @@ function dangerousStyleValue(name, value, isCustomProperty) {
     return value + 'px'; // Presumes implicit 'px' suffix for unitless numbers
   }
 
-  return ('' + value).trim();
+  return (''.concat(value)).trim();
 }
 
 export default dangerousStyleValue;
diff --git a/packages/react-dom/src/test-utils/ReactTestUtils.js b/packages/react-dom/src/test-utils/ReactTestUtils.js
index f93c92a93767c4..0dba33af31c703 100644
--- a/packages/react-dom/src/test-utils/ReactTestUtils.js
+++ b/packages/react-dom/src/test-utils/ReactTestUtils.js
@@ -95,7 +95,7 @@ function validateClassInstance(inst, methodName) {
     return;
   }
   let received;
-  const stringified = '' + inst;
+  const stringified = ''.concat(inst);
   if (isArray(inst)) {
     received = 'an array';
   } else if (inst && inst.nodeType === ELEMENT_NODE && inst.tagName) {
diff --git a/packages/react-noop-renderer/flight-modules.js b/packages/react-noop-renderer/flight-modules.js
index b9a2f4927458a1..abc9a59935df62 100644
--- a/packages/react-noop-renderer/flight-modules.js
+++ b/packages/react-noop-renderer/flight-modules.js
@@ -13,7 +13,7 @@ const modules: Map<string, Function> = new Map();
 
 // This simulates what the compiler will do when it replaces render functions with server blocks.
 export function saveModule(render: Function): string {
-  const idx = '' + moduleIdx++;
+  const idx = ''.concat(moduleIdx++);
   modules.set(idx, render);
   return idx;
 }
diff --git a/packages/react-noop-renderer/npm/flight-modules.js b/packages/react-noop-renderer/npm/flight-modules.js
index f4079d79538312..331942c1403dd2 100644
--- a/packages/react-noop-renderer/npm/flight-modules.js
+++ b/packages/react-noop-renderer/npm/flight-modules.js
@@ -6,7 +6,7 @@ var modules = new Map();
 
 // This simulates what the compiler will do when it replaces render functions with server blocks.
 exports.saveModule = function saveModule(render) {
-  var idx = '' + moduleIdx++;
+  var idx = ''.concat(moduleIdx++);
   modules.set(idx, render);
   return idx;
 };
diff --git a/packages/react-noop-renderer/src/createReactNoop.js b/packages/react-noop-renderer/src/createReactNoop.js
index 9e2c1ba7f876ce..df9b3fc774f6f2 100644
--- a/packages/react-noop-renderer/src/createReactNoop.js
+++ b/packages/react-noop-renderer/src/createReactNoop.js
@@ -935,7 +935,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     // TODO: Replace ReactNoop.render with createRoot + root.render
     createRoot() {
       const container = {
-        rootID: '' + idCounter++,
+        rootID: ''.concat(idCounter++),
         pendingChildren: [],
         children: [],
       };
@@ -962,7 +962,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
 
     createLegacyRoot() {
       const container = {
-        rootID: '' + idCounter++,
+        rootID: ''.concat(idCounter++),
         pendingChildren: [],
         children: [],
       };
diff --git a/packages/react-reconciler/src/ReactChildFiber.new.js b/packages/react-reconciler/src/ReactChildFiber.new.js
index e3f41115f53f98..e85e9afdd0ba72 100644
--- a/packages/react-reconciler/src/ReactChildFiber.new.js
+++ b/packages/react-reconciler/src/ReactChildFiber.new.js
@@ -163,7 +163,7 @@ function coerceRef(
           'bug in React. Please file an issue.',
         mixedRef,
       );
-      const stringRef = '' + mixedRef;
+      const stringRef = ''.concat(mixedRef);
       // Check if previous string ref matches new string ref
       if (
         current !== null &&
@@ -477,7 +477,7 @@ function ChildReconciler(shouldTrackSideEffects) {
       // we can continue to replace it without aborting even if it is not a text
       // node.
       const created = createFiberFromText(
-        '' + newChild,
+        ''.concat(newChild),
         returnFiber.mode,
         lanes,
       );
@@ -555,7 +555,7 @@ function ChildReconciler(shouldTrackSideEffects) {
       if (key !== null) {
         return null;
       }
-      return updateTextNode(returnFiber, oldFiber, '' + newChild, lanes);
+      return updateTextNode(returnFiber, oldFiber, ''.concat(newChild), lanes);
     }
 
     if (typeof newChild === 'object' && newChild !== null) {
@@ -614,7 +614,7 @@ function ChildReconciler(shouldTrackSideEffects) {
       // Text nodes don't have keys, so we neither have to check the old nor
       // new node for the key. If both are text nodes, they match.
       const matchedFiber = existingChildren.get(newIdx) || null;
-      return updateTextNode(returnFiber, matchedFiber, '' + newChild, lanes);
+      return updateTextNode(returnFiber, matchedFiber, ''.concat(newChild), lanes);
     }
 
     if (typeof newChild === 'object' && newChild !== null) {
@@ -1283,7 +1283,7 @@ function ChildReconciler(shouldTrackSideEffects) {
         reconcileSingleTextNode(
           returnFiber,
           currentFirstChild,
-          '' + newChild,
+          ''.concat(newChild),
           lanes,
         ),
       );
diff --git a/packages/react-reconciler/src/ReactChildFiber.old.js b/packages/react-reconciler/src/ReactChildFiber.old.js
index f1e39112b589b5..397de2934f7691 100644
--- a/packages/react-reconciler/src/ReactChildFiber.old.js
+++ b/packages/react-reconciler/src/ReactChildFiber.old.js
@@ -163,7 +163,7 @@ function coerceRef(
           'bug in React. Please file an issue.',
         mixedRef,
       );
-      const stringRef = '' + mixedRef;
+      const stringRef = ''.concat(mixedRef);
       // Check if previous string ref matches new string ref
       if (
         current !== null &&
@@ -477,7 +477,7 @@ function ChildReconciler(shouldTrackSideEffects) {
       // we can continue to replace it without aborting even if it is not a text
       // node.
       const created = createFiberFromText(
-        '' + newChild,
+        ''.concat(newChild),
         returnFiber.mode,
         lanes,
       );
@@ -555,7 +555,7 @@ function ChildReconciler(shouldTrackSideEffects) {
       if (key !== null) {
         return null;
       }
-      return updateTextNode(returnFiber, oldFiber, '' + newChild, lanes);
+      return updateTextNode(returnFiber, oldFiber, ''.concat(newChild), lanes);
     }
 
     if (typeof newChild === 'object' && newChild !== null) {
@@ -614,7 +614,7 @@ function ChildReconciler(shouldTrackSideEffects) {
       // Text nodes don't have keys, so we neither have to check the old nor
       // new node for the key. If both are text nodes, they match.
       const matchedFiber = existingChildren.get(newIdx) || null;
-      return updateTextNode(returnFiber, matchedFiber, '' + newChild, lanes);
+      return updateTextNode(returnFiber, matchedFiber, ''.concat(newChild), lanes);
     }
 
     if (typeof newChild === 'object' && newChild !== null) {
@@ -1283,7 +1283,7 @@ function ChildReconciler(shouldTrackSideEffects) {
         reconcileSingleTextNode(
           returnFiber,
           currentFirstChild,
-          '' + newChild,
+          ''.concat(newChild),
           lanes,
         ),
       );
diff --git a/packages/react-reconciler/src/ReactPortal.js b/packages/react-reconciler/src/ReactPortal.js
index 43f590c19d4a64..66d097df207c15 100644
--- a/packages/react-reconciler/src/ReactPortal.js
+++ b/packages/react-reconciler/src/ReactPortal.js
@@ -21,7 +21,7 @@ export function createPortal(
   return {
     // This tag allow us to uniquely identify this as a React Portal
     $$typeof: REACT_PORTAL_TYPE,
-    key: key == null ? null : '' + key,
+    key: key == null ? null : ''.concat(key),
     children,
     containerInfo,
     implementation,
diff --git a/packages/react-reconciler/src/__tests__/ReactIncremental-test.js b/packages/react-reconciler/src/__tests__/ReactIncremental-test.js
index 864723e927b8f9..a6708fcc9a8726 100644
--- a/packages/react-reconciler/src/__tests__/ReactIncremental-test.js
+++ b/packages/react-reconciler/src/__tests__/ReactIncremental-test.js
@@ -1110,7 +1110,7 @@ describe('ReactIncremental', () => {
       }
       render() {
         Scheduler.unstable_yieldValue('Bar:' + this.props.x);
-        return <span prop={'' + (this.props.x === this.state.y)} />;
+        return <span prop={''.concat(this.props.x === this.state.y)} />;
       }
     }
 
@@ -1159,7 +1159,7 @@ describe('ReactIncremental', () => {
         Scheduler.unstable_yieldValue(
           'Bar:' + this.props.x + '-' + this.props.step,
         );
-        return <span prop={'' + (this.props.x === this.state.y)} />;
+        return <span prop={''.concat(this.props.x === this.state.y)} />;
       }
     }
 
diff --git a/packages/react-reconciler/src/__tests__/ReactMemo-test.js b/packages/react-reconciler/src/__tests__/ReactMemo-test.js
index 639daeb1a98d1f..c6c2ddad5288cb 100644
--- a/packages/react-reconciler/src/__tests__/ReactMemo-test.js
+++ b/packages/react-reconciler/src/__tests__/ReactMemo-test.js
@@ -223,7 +223,7 @@ describe('memo', () => {
         class CounterInner extends React.Component {
           static defaultProps = {suffix: '!'};
           render() {
-            return <Text text={this.props.count + '' + this.props.suffix} />;
+            return <Text text={this.props.count + ''.concat(this.props.suffix)} />;
           }
         }
         const Counter = memo(CounterInner);
diff --git a/packages/react-reconciler/src/__tests__/ReactPersistent-test.js b/packages/react-reconciler/src/__tests__/ReactPersistent-test.js
index 46ccfea5c20619..bdaa0ea154052b 100644
--- a/packages/react-reconciler/src/__tests__/ReactPersistent-test.js
+++ b/packages/react-reconciler/src/__tests__/ReactPersistent-test.js
@@ -27,7 +27,7 @@ describe('ReactPersistent', () => {
   function createPortal(children, containerInfo, implementation, key) {
     return {
       $$typeof: Symbol.for('react.portal'),
-      key: key == null ? null : '' + key,
+      key: key == null ? null : ''.concat(key),
       children,
       containerInfo,
       implementation,
diff --git a/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js b/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
index 85eace536ac4ef..c0973883693bc6 100644
--- a/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
+++ b/packages/react-server-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
@@ -86,7 +86,7 @@ function convertModelToJSON(
     if (isArray(json)) {
       const jsonArray: Array<JSONValue> = [];
       for (let i = 0; i < json.length; i++) {
-        jsonArray[i] = convertModelToJSON(request, json, '' + i, json[i]);
+        jsonArray[i] = convertModelToJSON(request, json, ''.concat(i), json[i]);
       }
       return jsonArray;
     } else {
diff --git a/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js b/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js
index a81aec2c173843..429246b5712f2a 100644
--- a/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js
+++ b/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js
@@ -149,7 +149,7 @@ export default class ReactFlightWebpackPlugin {
             for (let i = 0; i < resolvedClientReferences.length; i++) {
               const dep = resolvedClientReferences[i];
               const chunkName = this.chunkName
-                .replace(/\[index\]/g, '' + i)
+                .replace(/\[index\]/g, ''.concat(i))
                 .replace(/\[request\]/g, Template.toPath(dep.userRequest));
 
               const block = new AsyncDependenciesBlock(
diff --git a/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOM-test.js b/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOM-test.js
index 12a50fce2187e3..3688a3d1e2c065 100644
--- a/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOM-test.js
+++ b/packages/react-server-dom-webpack/src/__tests__/ReactFlightDOM-test.js
@@ -69,7 +69,7 @@ describe('ReactFlightDOM', () => {
     };
     webpackMap['path/' + idx] = {
       default: {
-        id: '' + idx,
+        id: ''.concat(idx),
         chunks: [],
         name: 'd',
       },
diff --git a/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js b/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
index 0624e693cfe164..46645e266b687a 100644
--- a/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
+++ b/packages/react-server-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
@@ -83,7 +83,7 @@ function convertModelToJSON(
     if (isArray(json)) {
       const jsonArray: Array<JSONValue> = [];
       for (let i = 0; i < json.length; i++) {
-        jsonArray[i] = convertModelToJSON(request, json, '' + i, json[i]);
+        jsonArray[i] = convertModelToJSON(request, json, ''.concat(i), json[i]);
       }
       return jsonArray;
     } else {
diff --git a/packages/react-server/src/ReactFizzServer.js b/packages/react-server/src/ReactFizzServer.js
index 4b7eb46d94b483..bb84c80c7899dc 100644
--- a/packages/react-server/src/ReactFizzServer.js
+++ b/packages/react-server/src/ReactFizzServer.js
@@ -1188,7 +1188,7 @@ function renderNodeDestructive(
   if (typeof node === 'number') {
     pushTextInstance(
       task.blockedSegment.chunks,
-      '' + node,
+      ''.concat(node),
       request.responseState,
       task.assignID,
     );
diff --git a/packages/react-server/src/ReactFlightServer.js b/packages/react-server/src/ReactFlightServer.js
index dd5b43df2d35e7..51555916f25833 100644
--- a/packages/react-server/src/ReactFlightServer.js
+++ b/packages/react-server/src/ReactFlightServer.js
@@ -321,7 +321,7 @@ function describeObjectForErrorMessage(
       }
       const value = array[i];
       if (
-        '' + i === expandedName &&
+        ''.concat(i) === expandedName &&
         typeof value === 'object' &&
         value !== null
       ) {
@@ -615,8 +615,8 @@ function emitErrorChunk(request: Request, id: number, error: mixed): void {
   let stack = '';
   try {
     if (error instanceof Error) {
-      message = '' + error.message;
-      stack = '' + error.stack;
+      message = ''.concat(error.message);
+      stack = ''.concat(error.stack);
     } else {
       message = 'Error: ' + (error: any);
     }
diff --git a/packages/react-test-renderer/src/ReactTestRenderer.js b/packages/react-test-renderer/src/ReactTestRenderer.js
index 39c288014884d5..f10e6639bd1115 100644
--- a/packages/react-test-renderer/src/ReactTestRenderer.js
+++ b/packages/react-test-renderer/src/ReactTestRenderer.js
@@ -251,7 +251,7 @@ function getChildren(parent: Fiber) {
     if (validWrapperTypes.has(node.tag)) {
       children.push(wrapFiber(node));
     } else if (node.tag === HostText) {
-      children.push('' + node.memoizedProps);
+      children.push(''.concat(node.memoizedProps));
     } else {
       descend = true;
     }
diff --git a/packages/react/src/ReactChildren.js b/packages/react/src/ReactChildren.js
index 9acdc068e8ea33..fee87f3c065de9 100644
--- a/packages/react/src/ReactChildren.js
+++ b/packages/react/src/ReactChildren.js
@@ -65,7 +65,7 @@ function getElementKey(element: any, index: number): string {
   // that we don't block potential future ES APIs.
   if (typeof element === 'object' && element !== null && element.key != null) {
     // Explicit key
-    return escape('' + element.key);
+    return escape(''.concat(element.key));
   }
   // Implicit key determined by the index in the set
   return index.toString(36);
@@ -127,7 +127,7 @@ function mapIntoArray(
             // $FlowFixMe Flow incorrectly thinks React.Portal doesn't have a key
             (mappedChild.key && (!child || child.key !== mappedChild.key)
               ? // $FlowFixMe Flow incorrectly thinks existing element's key can be a number
-                escapeUserProvidedKey('' + mappedChild.key) + '/'
+                escapeUserProvidedKey(''.concat(mappedChild.key)) + '/'
               : '') +
             childKey,
         );
@@ -190,7 +190,7 @@ function mapIntoArray(
         );
       }
     } else if (type === 'object') {
-      const childrenString = '' + (children: any);
+      const childrenString = ''.concat((children: any));
       invariant(
         false,
         'Objects are not valid as a React child (found: %s). ' +
diff --git a/packages/react/src/ReactElement.js b/packages/react/src/ReactElement.js
index 75017cba37aeff..274fb4b16e18f9 100644
--- a/packages/react/src/ReactElement.js
+++ b/packages/react/src/ReactElement.js
@@ -222,11 +222,11 @@ export function jsx(type, config, maybeKey) {
   // <div {...props} key="Hi" />, because we aren't currently able to tell if
   // key is explicitly declared to be undefined or not.
   if (maybeKey !== undefined) {
-    key = '' + maybeKey;
+    key = ''.concat(maybeKey);
   }
 
   if (hasValidKey(config)) {
-    key = '' + config.key;
+    key = ''.concat(config.key);
   }
 
   if (hasValidRef(config)) {
@@ -286,11 +286,11 @@ export function jsxDEV(type, config, maybeKey, source, self) {
   // <div {...props} key="Hi" />, because we aren't currently able to tell if
   // key is explicitly declared to be undefined or not.
   if (maybeKey !== undefined) {
-    key = '' + maybeKey;
+    key = ''.concat(maybeKey);
   }
 
   if (hasValidKey(config)) {
-    key = '' + config.key;
+    key = ''.concat(config.key);
   }
 
   if (hasValidRef(config)) {
@@ -366,7 +366,7 @@ export function createElement(type, config, children) {
       }
     }
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     self = config.__self === undefined ? null : config.__self;
@@ -499,7 +499,7 @@ export function cloneElement(element, config, children) {
       owner = ReactCurrentOwner.current;
     }
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     // Remaining properties override existing props
diff --git a/packages/react/src/jsx/ReactJSXElement.js b/packages/react/src/jsx/ReactJSXElement.js
index e87a969712e1e8..faf3167d304104 100644
--- a/packages/react/src/jsx/ReactJSXElement.js
+++ b/packages/react/src/jsx/ReactJSXElement.js
@@ -222,11 +222,11 @@ export function jsx(type, config, maybeKey) {
   // <div {...props} key="Hi" />, because we aren't currently able to tell if
   // key is explicitly declared to be undefined or not.
   if (maybeKey !== undefined) {
-    key = '' + maybeKey;
+    key = ''.concat(maybeKey);
   }
 
   if (hasValidKey(config)) {
-    key = '' + config.key;
+    key = ''.concat(config.key);
   }
 
   if (hasValidRef(config)) {
@@ -287,11 +287,11 @@ export function jsxDEV(type, config, maybeKey, source, self) {
     // <div {...props} key="Hi" />, because we aren't currently able to tell if
     // key is explicitly declared to be undefined or not.
     if (maybeKey !== undefined) {
-      key = '' + maybeKey;
+      key = ''.concat(maybeKey);
     }
 
     if (hasValidKey(config)) {
-      key = '' + config.key;
+      key = ''.concat(config.key);
     }
 
     if (hasValidRef(config)) {
diff --git a/packages/shared/consoleWithStackDev.js b/packages/shared/consoleWithStackDev.js
index 72c7e76273a785..556c4d72114f9f 100644
--- a/packages/shared/consoleWithStackDev.js
+++ b/packages/shared/consoleWithStackDev.js
@@ -36,7 +36,7 @@ function printWarning(level, format, args) {
       args = args.concat([stack]);
     }
 
-    const argsWithFormat = args.map(item => '' + item);
+    const argsWithFormat = args.map(item => ''.concat(item));
     // Careful: RN currently depends on this prefix
     argsWithFormat.unshift('Warning: ' + format);
     // We intentionally don't use spread (or .apply) directly because it
diff --git a/scripts/error-codes/extract-errors.js b/scripts/error-codes/extract-errors.js
index 58823cbe16873b..475b6c01bc7a29 100644
--- a/scripts/error-codes/extract-errors.js
+++ b/scripts/error-codes/extract-errors.js
@@ -87,7 +87,7 @@ module.exports = function(opts) {
     if (existingErrorMap.hasOwnProperty(errorMsgLiteral)) {
       return;
     }
-    existingErrorMap[errorMsgLiteral] = '' + currentID++;
+    existingErrorMap[errorMsgLiteral] = ''.concat(currentID++);
   }
 
   function flush(cb) {
diff --git a/scripts/eslint-rules/__tests__/no-primitive-constructors-test.internal.js b/scripts/eslint-rules/__tests__/no-primitive-constructors-test.internal.js
index c440b30920f3fe..b3296467675fc8 100644
--- a/scripts/eslint-rules/__tests__/no-primitive-constructors-test.internal.js
+++ b/scripts/eslint-rules/__tests__/no-primitive-constructors-test.internal.js
@@ -14,7 +14,7 @@ const RuleTester = require('eslint').RuleTester;
 const ruleTester = new RuleTester();
 
 ruleTester.run('eslint-rules/no-primitive-constructors', rule, {
-  valid: ['!!obj', "'' + obj", '+string'],
+  valid: ['!!obj', "''.concat(obj)", '+string'],
   invalid: [
     {
       code: 'Boolean(obj)',
@@ -32,7 +32,7 @@ ruleTester.run('eslint-rules/no-primitive-constructors', rule, {
           message:
             'Do not use the String constructor. ' +
             'To cast a value to a string, concat it with the empty string ' +
-            "(unless it's a symbol, which has different semantics): '' + value",
+            "(unless it's a symbol, which has different semantics): ''.concat(value)",
         },
       ],
     },
diff --git a/scripts/eslint-rules/no-primitive-constructors.js b/scripts/eslint-rules/no-primitive-constructors.js
index 51ddde284e747c..f012d1099d93bc 100644
--- a/scripts/eslint-rules/no-primitive-constructors.js
+++ b/scripts/eslint-rules/no-primitive-constructors.js
@@ -30,7 +30,7 @@ module.exports = function(context) {
           name,
           'To cast a value to a string, concat it with the empty string ' +
             "(unless it's a symbol, which has different semantics): " +
-            "'' + value"
+            "''.concat(value)"
         );
         break;
       case 'Number':
diff --git a/scripts/merge-fork/merge-fork.js b/scripts/merge-fork/merge-fork.js
index ccefc8c0d0b6eb..ddbd8b6c452586 100644
--- a/scripts/merge-fork/merge-fork.js
+++ b/scripts/merge-fork/merge-fork.js
@@ -90,7 +90,7 @@ for (const {base: baseFilename, from, to} of getTransforms()) {
     }
   );
   if (gitShowResult.status !== 0) {
-    console.error('' + gitShowResult.stderr);
+    console.error(''.concat(gitShowResult.stderr));
     continue;
   }
 
@@ -104,6 +104,6 @@ for (const {base: baseFilename, from, to} of getTransforms()) {
   });
 
   if (mergeFileResult.status !== 0) {
-    console.error('' + mergeFileResult.stderr);
+    console.error(''.concat(mergeFileResult.stderr));
   }
 }