From ec5f634f299a42b2fc19db2272f8204a47c6004c Mon Sep 17 00:00:00 2001
From: kingwl <kingwenlu@gmail.com>
Date: Tue, 22 Sep 2020 17:28:35 +0800
Subject: [PATCH 1/9] Add item method

---
 src/compiler/commandLineParser.ts             |  1 +
 src/lib/esnext.array.d.ts                     | 88 +++++++++++++++++++
 src/lib/esnext.d.ts                           |  1 +
 src/lib/esnext.string.d.ts                    |  6 ++
 src/lib/libs.json                             |  1 +
 .../config/convertCompilerOptionsFromJson.ts  |  8 +-
 6 files changed, 101 insertions(+), 4 deletions(-)
 create mode 100644 src/lib/esnext.array.d.ts

diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index beb601b0b8f6f..5e5a83f85cff7 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -72,6 +72,7 @@ namespace ts {
         ["esnext.asynciterable", "lib.es2018.asynciterable.d.ts"],
         ["esnext.intl", "lib.esnext.intl.d.ts"],
         ["esnext.bigint", "lib.es2020.bigint.d.ts"],
+        ["esnext.array", "lib.esnext.array.d.ts"],
         ["esnext.string", "lib.esnext.string.d.ts"],
         ["esnext.promise", "lib.esnext.promise.d.ts"]
     ];
diff --git a/src/lib/esnext.array.d.ts b/src/lib/esnext.array.d.ts
new file mode 100644
index 0000000000000..ace687ca91049
--- /dev/null
+++ b/src/lib/esnext.array.d.ts
@@ -0,0 +1,88 @@
+interface Array<T> {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): T | undefined;
+}
+
+
+interface ReadonlyArray<T> {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): T | undefined;
+}
+
+interface Int8Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Uint8Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Uint8ClampedArray {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Int16Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Uint16Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Int32Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Uint32Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Float32Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
+
+interface Float64Array {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): number | undefined;
+}
diff --git a/src/lib/esnext.d.ts b/src/lib/esnext.d.ts
index 36c759ff9123c..10dcba251707f 100644
--- a/src/lib/esnext.d.ts
+++ b/src/lib/esnext.d.ts
@@ -1,4 +1,5 @@
 /// <reference lib="es2020" />
 /// <reference lib="esnext.intl" />
 /// <reference lib="esnext.string" />
+/// <reference lib="esnext.array" />
 /// <reference lib="esnext.promise" />
diff --git a/src/lib/esnext.string.d.ts b/src/lib/esnext.string.d.ts
index 66971bf84d6cf..df8a49f3be94e 100644
--- a/src/lib/esnext.string.d.ts
+++ b/src/lib/esnext.string.d.ts
@@ -12,4 +12,10 @@ interface String {
      * @param replacer A function that returns the replacement text.
      */
     replaceAll(searchValue: string | RegExp, replacer: (substring: string, ...args: any[]) => string): string;
+
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+    item(index: number): string | undefined;
 }
diff --git a/src/lib/libs.json b/src/lib/libs.json
index 574c8b27c3730..7eccfcab4dad5 100644
--- a/src/lib/libs.json
+++ b/src/lib/libs.json
@@ -47,6 +47,7 @@
         "es2020.string",
         "es2020.symbol.wellknown",
         "es2020.intl",
+        "esnext.array",
         "esnext.intl",
         "esnext.string",
         "esnext.promise",
diff --git a/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts b/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
index d007ccf5f8482..1478d050cefed 100644
--- a/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
+++ b/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
@@ -295,7 +295,7 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.bigint', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]
@@ -326,7 +326,7 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]
@@ -357,7 +357,7 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]
@@ -388,7 +388,7 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]

From b3daf96e8d83ff3255ec6321e2f0510167177e0d Mon Sep 17 00:00:00 2001
From: kingwl <kingwenlu@gmail.com>
Date: Tue, 22 Sep 2020 17:31:43 +0800
Subject: [PATCH 2/9] fix jsdoc

---
 src/lib/esnext.array.d.ts | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/lib/esnext.array.d.ts b/src/lib/esnext.array.d.ts
index ace687ca91049..ba0fe1217c746 100644
--- a/src/lib/esnext.array.d.ts
+++ b/src/lib/esnext.array.d.ts
@@ -1,6 +1,6 @@
 interface Array<T> {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): T | undefined;
@@ -9,7 +9,7 @@ interface Array<T> {
 
 interface ReadonlyArray<T> {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): T | undefined;
@@ -17,7 +17,7 @@ interface ReadonlyArray<T> {
 
 interface Int8Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -25,7 +25,7 @@ interface Int8Array {
 
 interface Uint8Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -33,7 +33,7 @@ interface Uint8Array {
 
 interface Uint8ClampedArray {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -41,7 +41,7 @@ interface Uint8ClampedArray {
 
 interface Int16Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -49,7 +49,7 @@ interface Int16Array {
 
 interface Uint16Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -57,7 +57,7 @@ interface Uint16Array {
 
 interface Int32Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -65,7 +65,7 @@ interface Int32Array {
 
 interface Uint32Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -73,7 +73,7 @@ interface Uint32Array {
 
 interface Float32Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;
@@ -81,7 +81,7 @@ interface Float32Array {
 
 interface Float64Array {
     /**
-     * Access string by relative indexing.
+     * Access item by relative indexing.
      * @param index index to access.
      */
     item(index: number): number | undefined;

From b44a0071314626b215ccd66c2fe162bbebbb5b12 Mon Sep 17 00:00:00 2001
From: kingwl <kingwenlu@gmail.com>
Date: Tue, 22 Sep 2020 21:50:50 +0800
Subject: [PATCH 3/9] accept baseline

---
 .../reference/importExportInternalComments.symbols   |  2 +-
 .../reference/keyofAndIndexedAccess2.symbols         | 12 ++++++------
 .../reference/noIterationTypeErrorsInCFA.symbols     |  2 +-
 .../taggedTemplatesWithTypeArguments1.symbols        |  2 +-
 .../reference/typeGuardConstructorNarrowAny.symbols  |  2 +-
 .../typeGuardConstructorPrimitiveTypes.symbols       |  2 +-
 6 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/tests/baselines/reference/importExportInternalComments.symbols b/tests/baselines/reference/importExportInternalComments.symbols
index 87eeb2d31e9c9..e4c5f85d9bd77 100644
--- a/tests/baselines/reference/importExportInternalComments.symbols
+++ b/tests/baselines/reference/importExportInternalComments.symbols
@@ -4,7 +4,7 @@ declare module "foo";
 
 === tests/cases/compiler/default.ts ===
 /*1*/ export /*2*/ default /*3*/ Array /*4*/;
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 
 === tests/cases/compiler/index.ts ===
 /*1*/ import /*2*/ D /*3*/, /*4*/ { /*5*/ A /*6*/, /*7*/ B /*8*/ as /*9*/ C /*10*/ } /*11*/ from /*12*/ "foo";
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.symbols b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
index 58b5f470c030b..a061d9f3003e8 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.symbols
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
@@ -440,9 +440,9 @@ function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(par
 >fn : Symbol(fn, Decl(keyofAndIndexedAccess2.ts, 115, 69))
 >T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 119, 12))
 >elements : Symbol(elements, Decl(keyofAndIndexedAccess2.ts, 119, 23))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 >elements : Symbol(elements, Decl(keyofAndIndexedAccess2.ts, 119, 51))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 >param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 119, 77))
 >T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 119, 12))
 >cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 119, 86))
@@ -459,7 +459,7 @@ function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(par
 function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
 >fn2 : Symbol(fn2, Decl(keyofAndIndexedAccess2.ts, 121, 1))
 >T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 123, 13))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 >param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 123, 38))
 >T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 123, 13))
 >cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 123, 47))
@@ -476,7 +476,7 @@ function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void
 function fn3<T extends ReadonlyArray<string>>(param: T, cb: (element: T[number]) => void) {
 >fn3 : Symbol(fn3, Decl(keyofAndIndexedAccess2.ts, 125, 1))
 >T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 129, 13))
->ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --))
+>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --) ... and 1 more)
 >param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 129, 46))
 >T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 129, 13))
 >cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 129, 55))
@@ -494,12 +494,12 @@ function fn4<K extends number>() {
 
     let x: Array<string>[K] = 'abc';
 >x : Symbol(x, Decl(keyofAndIndexedAccess2.ts, 134, 7))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 >K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 133, 13))
 
     let y: ReadonlyArray<string>[K] = 'abc';
 >y : Symbol(y, Decl(keyofAndIndexedAccess2.ts, 135, 7))
->ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --))
+>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --) ... and 1 more)
 >K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 133, 13))
 }
 
diff --git a/tests/baselines/reference/noIterationTypeErrorsInCFA.symbols b/tests/baselines/reference/noIterationTypeErrorsInCFA.symbols
index 3498f52d456f3..60040c3ed17c4 100644
--- a/tests/baselines/reference/noIterationTypeErrorsInCFA.symbols
+++ b/tests/baselines/reference/noIterationTypeErrorsInCFA.symbols
@@ -13,7 +13,7 @@ export function doRemove(dds: F | F[]) {
 
     if (!Array.isArray(dds)) {
 >Array.isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 >isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
 >dds : Symbol(dds, Decl(noIterationTypeErrorsInCFA.ts, 3, 25))
 
diff --git a/tests/baselines/reference/taggedTemplatesWithTypeArguments1.symbols b/tests/baselines/reference/taggedTemplatesWithTypeArguments1.symbols
index 4cd6dce23e368..f37166423f17c 100644
--- a/tests/baselines/reference/taggedTemplatesWithTypeArguments1.symbols
+++ b/tests/baselines/reference/taggedTemplatesWithTypeArguments1.symbols
@@ -5,7 +5,7 @@ declare function f<T>(strs: TemplateStringsArray, ...callbacks: Array<(x: T) =>
 >strs : Symbol(strs, Decl(taggedTemplatesWithTypeArguments1.ts, 0, 22))
 >TemplateStringsArray : Symbol(TemplateStringsArray, Decl(lib.es5.d.ts, --, --))
 >callbacks : Symbol(callbacks, Decl(taggedTemplatesWithTypeArguments1.ts, 0, 49))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 >x : Symbol(x, Decl(taggedTemplatesWithTypeArguments1.ts, 0, 71))
 >T : Symbol(T, Decl(taggedTemplatesWithTypeArguments1.ts, 0, 19))
 
diff --git a/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols b/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols
index acbc179aa270d..88c2e6893d0f6 100644
--- a/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols
+++ b/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols
@@ -26,7 +26,7 @@ if (var1.constructor === Boolean) {
 }
 if (var1.constructor === Array) {
 >var1 : Symbol(var1, Decl(typeGuardConstructorNarrowAny.ts, 1, 3))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 
     var1; // any[]
 >var1 : Symbol(var1, Decl(typeGuardConstructorNarrowAny.ts, 1, 3))
diff --git a/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols b/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols
index 1bcc2f586eb5e..699026eb4781d 100644
--- a/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols
+++ b/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols
@@ -34,7 +34,7 @@ if (var1.constructor === Array) {
 >var1.constructor : Symbol(Object.constructor, Decl(lib.es5.d.ts, --, --))
 >var1 : Symbol(var1, Decl(typeGuardConstructorPrimitiveTypes.ts, 1, 3))
 >constructor : Symbol(Object.constructor, Decl(lib.es5.d.ts, --, --))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 
     var1; // any[]
 >var1 : Symbol(var1, Decl(typeGuardConstructorPrimitiveTypes.ts, 1, 3))

From 93ee38fe86f3b3b43ad8d3838c7c6ad4c1cf39a2 Mon Sep 17 00:00:00 2001
From: kingwl <kingwenlu@gmail.com>
Date: Wed, 9 Jun 2021 12:02:41 +0800
Subject: [PATCH 4/9] Rename item method

---
 src/compiler/commandLineParser.ts             |  4 ++--
 src/lib/es2021.string.d.ts                    |  6 -----
 src/lib/esnext.array.d.ts                     | 22 ++++++++---------
 src/lib/esnext.d.ts                           |  1 +
 src/lib/esnext.string.d.ts                    |  7 ++++++
 src/lib/libs.json                             |  3 ++-
 .../config/convertCompilerOptionsFromJson.ts  | 24 +++++++++++++++----
 .../reference/callWithSpread4.symbols         |  4 ++--
 .../flatArrayNoExcessiveStackDepth.symbols    |  2 +-
 ...tatus.DiagnosticsPresent_OutputsSkipped.js |  2 +-
 .../typeGuardConstructorNarrowAny.symbols     |  2 +-
 ...typeGuardConstructorPrimitiveTypes.symbols |  6 ++---
 12 files changed, 51 insertions(+), 32 deletions(-)
 create mode 100644 src/lib/esnext.string.d.ts

diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 0897e93a2a80c..93a7deb070108 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -71,15 +71,15 @@ namespace ts {
         ["es2021.promise", "lib.es2021.promise.d.ts"],
         ["es2021.string", "lib.es2021.string.d.ts"],
         ["es2021.weakref", "lib.es2021.weakref.d.ts"],
-        ["esnext.array", "lib.es2019.array.d.ts"],
+        ["es2021.string", "lib.es2021.string.d.ts"],
         ["esnext.symbol", "lib.es2019.symbol.d.ts"],
         ["esnext.asynciterable", "lib.es2018.asynciterable.d.ts"],
         ["esnext.intl", "lib.esnext.intl.d.ts"],
         ["esnext.bigint", "lib.es2020.bigint.d.ts"],
-        ["esnext.string", "lib.es2021.string.d.ts"],
         ["esnext.promise", "lib.es2021.promise.d.ts"],
         ["esnext.weakref", "lib.es2021.weakref.d.ts"],
         ["esnext.array", "lib.esnext.array.d.ts"],
+        ["esnext.string", "lib.esnext.string.d.ts"],
     ];
 
     /**
diff --git a/src/lib/es2021.string.d.ts b/src/lib/es2021.string.d.ts
index df8a49f3be94e..66971bf84d6cf 100644
--- a/src/lib/es2021.string.d.ts
+++ b/src/lib/es2021.string.d.ts
@@ -12,10 +12,4 @@ interface String {
      * @param replacer A function that returns the replacement text.
      */
     replaceAll(searchValue: string | RegExp, replacer: (substring: string, ...args: any[]) => string): string;
-
-    /**
-     * Access string by relative indexing.
-     * @param index index to access.
-     */
-    item(index: number): string | undefined;
 }
diff --git a/src/lib/esnext.array.d.ts b/src/lib/esnext.array.d.ts
index ba0fe1217c746..f7e58a28f156f 100644
--- a/src/lib/esnext.array.d.ts
+++ b/src/lib/esnext.array.d.ts
@@ -3,7 +3,7 @@ interface Array<T> {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): T | undefined;
+    at(index: number): T | undefined;
 }
 
 
@@ -12,7 +12,7 @@ interface ReadonlyArray<T> {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): T | undefined;
+    at(index: number): T | undefined;
 }
 
 interface Int8Array {
@@ -20,7 +20,7 @@ interface Int8Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Uint8Array {
@@ -28,7 +28,7 @@ interface Uint8Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Uint8ClampedArray {
@@ -36,7 +36,7 @@ interface Uint8ClampedArray {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Int16Array {
@@ -44,7 +44,7 @@ interface Int16Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Uint16Array {
@@ -52,7 +52,7 @@ interface Uint16Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Int32Array {
@@ -60,7 +60,7 @@ interface Int32Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Uint32Array {
@@ -68,7 +68,7 @@ interface Uint32Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Float32Array {
@@ -76,7 +76,7 @@ interface Float32Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
 
 interface Float64Array {
@@ -84,5 +84,5 @@ interface Float64Array {
      * Access item by relative indexing.
      * @param index index to access.
      */
-    item(index: number): number | undefined;
+    at(index: number): number | undefined;
 }
diff --git a/src/lib/esnext.d.ts b/src/lib/esnext.d.ts
index 5f35a02d5423f..9ad61073d9550 100644
--- a/src/lib/esnext.d.ts
+++ b/src/lib/esnext.d.ts
@@ -1,3 +1,4 @@
 /// <reference lib="es2021" />
 /// <reference lib="esnext.intl" />
 /// <reference lib="esnext.array" />
+/// <reference lib="esnext.string" />
diff --git a/src/lib/esnext.string.d.ts b/src/lib/esnext.string.d.ts
new file mode 100644
index 0000000000000..09db1f6372a65
--- /dev/null
+++ b/src/lib/esnext.string.d.ts
@@ -0,0 +1,7 @@
+interface String {
+    /**
+     * Access string by relative indexing.
+     * @param index index to access.
+     */
+     item(index: number): string | undefined;
+}
\ No newline at end of file
diff --git a/src/lib/libs.json b/src/lib/libs.json
index b86aa55a12ab9..3d8f1f1171277 100644
--- a/src/lib/libs.json
+++ b/src/lib/libs.json
@@ -51,8 +51,9 @@
         "es2021.string",
         "es2021.promise",
         "es2021.weakref",
-        "esnext.array",
         "esnext.intl",
+        "esnext.array",
+        "esnext.string",
         // Default libraries
         "es5.full",
         "es2015.full",
diff --git a/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts b/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
index 760938b57325e..2b9011930e66f 100644
--- a/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
+++ b/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
@@ -295,7 +295,11 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', " +
+                            "'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', " + 
+                            "'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', " +
+                            "'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', " +
+                            "'esnext.array', 'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]
@@ -326,7 +330,11 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', " +
+                            "'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', " +
+                            "'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', " +
+                            "'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', " +
+                            "'esnext.array', 'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]
@@ -357,7 +365,11 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', " +
+                        "'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', " +
+                        "'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', " +
+                        "'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', " +
+                        "'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]
@@ -388,7 +400,11 @@ namespace ts {
                         file: undefined,
                         start: 0,
                         length: 0,
-                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', 'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', 'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', 'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', 'esnext.array', 'esnext.string', 'esnext.promise'.",
+                        messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', " +
+                        "'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', " +
+                        "'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', " +
+                        "'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', " +
+                        "'esnext.array', 'esnext.string', 'esnext.promise'.",
                         code: Diagnostics.Argument_for_0_option_must_be_Colon_1.code,
                         category: Diagnostics.Argument_for_0_option_must_be_Colon_1.category
                     }]
diff --git a/tests/baselines/reference/callWithSpread4.symbols b/tests/baselines/reference/callWithSpread4.symbols
index 5c3e96596ef60..da89faff58547 100644
--- a/tests/baselines/reference/callWithSpread4.symbols
+++ b/tests/baselines/reference/callWithSpread4.symbols
@@ -30,7 +30,7 @@ declare const pli: {
 
     (streams: ReadonlyArray<R | W | RW>): Promise<void>;
 >streams : Symbol(streams, Decl(callWithSpread4.ts, 5, 5))
->ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --))
+>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --) ... and 1 more)
 >R : Symbol(R, Decl(callWithSpread4.ts, 0, 0))
 >W : Symbol(W, Decl(callWithSpread4.ts, 0, 22))
 >RW : Symbol(RW, Decl(callWithSpread4.ts, 1, 22))
@@ -43,7 +43,7 @@ declare const pli: {
 >RW : Symbol(RW, Decl(callWithSpread4.ts, 1, 22))
 >W : Symbol(W, Decl(callWithSpread4.ts, 0, 22))
 >streams : Symbol(streams, Decl(callWithSpread4.ts, 6, 23))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 >RW : Symbol(RW, Decl(callWithSpread4.ts, 1, 22))
 >W : Symbol(W, Decl(callWithSpread4.ts, 0, 22))
 >Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2018.promise.d.ts, --, --))
diff --git a/tests/baselines/reference/flatArrayNoExcessiveStackDepth.symbols b/tests/baselines/reference/flatArrayNoExcessiveStackDepth.symbols
index 4b27f6006cbd7..bbd3083d04c40 100644
--- a/tests/baselines/reference/flatArrayNoExcessiveStackDepth.symbols
+++ b/tests/baselines/reference/flatArrayNoExcessiveStackDepth.symbols
@@ -15,7 +15,7 @@ const bar = foo.flatMap(bar => bar as Foo);
 
 interface Foo extends Array<string> {}
 >Foo : Symbol(Foo, Decl(flatArrayNoExcessiveStackDepth.ts, 3, 43))
->Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 3 more)
 
 // Repros from comments in #43249
 
diff --git a/tests/baselines/reference/tsc/runWithoutArgs/initial-build/show-help-with-ExitStatus.DiagnosticsPresent_OutputsSkipped.js b/tests/baselines/reference/tsc/runWithoutArgs/initial-build/show-help-with-ExitStatus.DiagnosticsPresent_OutputsSkipped.js
index 362d9209ea89e..f5a24714db2b3 100644
--- a/tests/baselines/reference/tsc/runWithoutArgs/initial-build/show-help-with-ExitStatus.DiagnosticsPresent_OutputsSkipped.js
+++ b/tests/baselines/reference/tsc/runWithoutArgs/initial-build/show-help-with-ExitStatus.DiagnosticsPresent_OutputsSkipped.js
@@ -26,7 +26,7 @@ Options:
  -t VERSION, --target VERSION                       Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', 'ES2021', or 'ESNEXT'.
  -m KIND, --module KIND                             Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'.
  --lib                                              Specify library files to be included in the compilation.
-                                                      'es5' 'es6' 'es2015' 'es7' 'es2016' 'es2017' 'es2018' 'es2019' 'es2020' 'es2021' 'esnext' 'dom' 'dom.iterable' 'webworker' 'webworker.importscripts' 'webworker.iterable' 'scripthost' 'es2015.core' 'es2015.collection' 'es2015.generator' 'es2015.iterable' 'es2015.promise' 'es2015.proxy' 'es2015.reflect' 'es2015.symbol' 'es2015.symbol.wellknown' 'es2016.array.include' 'es2017.object' 'es2017.sharedmemory' 'es2017.string' 'es2017.intl' 'es2017.typedarrays' 'es2018.asyncgenerator' 'es2018.asynciterable' 'es2018.intl' 'es2018.promise' 'es2018.regexp' 'es2019.array' 'es2019.object' 'es2019.string' 'es2019.symbol' 'es2020.bigint' 'es2020.promise' 'es2020.sharedmemory' 'es2020.string' 'es2020.symbol.wellknown' 'es2020.intl' 'es2021.promise' 'es2021.string' 'es2021.weakref' 'esnext.array' 'esnext.symbol' 'esnext.asynciterable' 'esnext.intl' 'esnext.bigint' 'esnext.string' 'esnext.promise' 'esnext.weakref' 
+                                                      'es5' 'es6' 'es2015' 'es7' 'es2016' 'es2017' 'es2018' 'es2019' 'es2020' 'es2021' 'esnext' 'dom' 'dom.iterable' 'webworker' 'webworker.importscripts' 'webworker.iterable' 'scripthost' 'es2015.core' 'es2015.collection' 'es2015.generator' 'es2015.iterable' 'es2015.promise' 'es2015.proxy' 'es2015.reflect' 'es2015.symbol' 'es2015.symbol.wellknown' 'es2016.array.include' 'es2017.object' 'es2017.sharedmemory' 'es2017.string' 'es2017.intl' 'es2017.typedarrays' 'es2018.asyncgenerator' 'es2018.asynciterable' 'es2018.intl' 'es2018.promise' 'es2018.regexp' 'es2019.array' 'es2019.object' 'es2019.string' 'es2019.symbol' 'es2020.bigint' 'es2020.promise' 'es2020.sharedmemory' 'es2020.string' 'es2020.symbol.wellknown' 'es2020.intl' 'es2021.promise' 'es2021.string' 'es2021.weakref' 'esnext.symbol' 'esnext.asynciterable' 'esnext.intl' 'esnext.bigint' 'esnext.promise' 'esnext.weakref' 'esnext.array' 'esnext.string' 
  --allowJs                                          Allow javascript files to be compiled.
  --jsx KIND                                         Specify JSX code generation: 'preserve', 'react-native', 'react', 'react-jsx' or 'react-jsxdev'.
  -d, --declaration                                  Generates corresponding '.d.ts' file.
diff --git a/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols b/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols
index 88c2e6893d0f6..980e68c3f1cf9 100644
--- a/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols
+++ b/tests/baselines/reference/typeGuardConstructorNarrowAny.symbols
@@ -5,7 +5,7 @@ let var1: any;
 
 if (var1.constructor === String) {
 >var1 : Symbol(var1, Decl(typeGuardConstructorNarrowAny.ts, 1, 3))
->String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 5 more)
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 6 more)
 
     var1; // String
 >var1 : Symbol(var1, Decl(typeGuardConstructorNarrowAny.ts, 1, 3))
diff --git a/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols b/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols
index 699026eb4781d..7258c198d18f7 100644
--- a/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols
+++ b/tests/baselines/reference/typeGuardConstructorPrimitiveTypes.symbols
@@ -7,7 +7,7 @@ if (var1.constructor === String) {
 >var1.constructor : Symbol(Object.constructor, Decl(lib.es5.d.ts, --, --))
 >var1 : Symbol(var1, Decl(typeGuardConstructorPrimitiveTypes.ts, 1, 3))
 >constructor : Symbol(Object.constructor, Decl(lib.es5.d.ts, --, --))
->String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 5 more)
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 6 more)
 
     var1; // string
 >var1 : Symbol(var1, Decl(typeGuardConstructorPrimitiveTypes.ts, 1, 3))
@@ -61,7 +61,7 @@ if (var1.constructor === BigInt) {
 // Narrow a union of primitive object types
 let var2: String | Number | Boolean | Symbol | BigInt;
 >var2 : Symbol(var2, Decl(typeGuardConstructorPrimitiveTypes.ts, 22, 3))
->String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 5 more)
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 6 more)
 >Number : Symbol(Number, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >Boolean : Symbol(Boolean, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2019.symbol.d.ts, --, --))
@@ -71,7 +71,7 @@ if (var2.constructor === String) {
 >var2.constructor : Symbol(Object.constructor, Decl(lib.es5.d.ts, --, --))
 >var2 : Symbol(var2, Decl(typeGuardConstructorPrimitiveTypes.ts, 22, 3))
 >constructor : Symbol(Object.constructor, Decl(lib.es5.d.ts, --, --))
->String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 5 more)
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --) ... and 6 more)
 
     var2; // String
 >var2 : Symbol(var2, Decl(typeGuardConstructorPrimitiveTypes.ts, 22, 3))

From 76e5e03f74ce7ccca58905adbaf28ba00bfbc4f8 Mon Sep 17 00:00:00 2001
From: kingwl <kingwenlu@gmail.com>
Date: Wed, 9 Jun 2021 12:07:16 +0800
Subject: [PATCH 5/9] Add bigint64 array

---
 src/lib/esnext.array.d.ts | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/lib/esnext.array.d.ts b/src/lib/esnext.array.d.ts
index f7e58a28f156f..f0cde2963d80a 100644
--- a/src/lib/esnext.array.d.ts
+++ b/src/lib/esnext.array.d.ts
@@ -86,3 +86,19 @@ interface Float64Array {
      */
     at(index: number): number | undefined;
 }
+
+interface BigInt64Array {
+    /**
+     * Access item by relative indexing.
+     * @param index index to access.
+     */
+    at(index: number): bigint | undefined;
+}
+
+interface BigUint64Array {
+    /**
+     * Access item by relative indexing.
+     * @param index index to access.
+     */
+     at(index: number): bigint | undefined;
+}

From aadb17dd77bba4e70c74fbba0c2f105a9d68119c Mon Sep 17 00:00:00 2001
From: kingwl <kingwenlu@gmail.com>
Date: Wed, 9 Jun 2021 12:07:42 +0800
Subject: [PATCH 6/9] Add whitespace

---
 src/lib/esnext.string.d.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lib/esnext.string.d.ts b/src/lib/esnext.string.d.ts
index 09db1f6372a65..fac0ace15a3a1 100644
--- a/src/lib/esnext.string.d.ts
+++ b/src/lib/esnext.string.d.ts
@@ -4,4 +4,4 @@ interface String {
      * @param index index to access.
      */
      item(index: number): string | undefined;
-}
\ No newline at end of file
+}

From 33df981e3a6e4224c5fa87c3c89daf02a8aad16a Mon Sep 17 00:00:00 2001
From: Wenlu Wang <kingwenlu@gmail.com>
Date: Wed, 9 Jun 2021 14:07:21 +0800
Subject: [PATCH 7/9] Update src/lib/esnext.string.d.ts

Co-authored-by: Anonymous <65428781+CrimsonCodes0@users.noreply.github.com>
---
 src/lib/esnext.string.d.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lib/esnext.string.d.ts b/src/lib/esnext.string.d.ts
index fac0ace15a3a1..7a398a35bf95f 100644
--- a/src/lib/esnext.string.d.ts
+++ b/src/lib/esnext.string.d.ts
@@ -3,5 +3,5 @@ interface String {
      * Access string by relative indexing.
      * @param index index to access.
      */
-     item(index: number): string | undefined;
+     at(index: number): string | undefined;
 }

From 7ee9c40d26b1364e8d52f98ab7e386d472271b94 Mon Sep 17 00:00:00 2001
From: kingwl <kingwenlu@gmail.com>
Date: Thu, 10 Jun 2021 11:44:51 +0800
Subject: [PATCH 8/9] Avoid whitespace

---
 .../unittests/config/convertCompilerOptionsFromJson.ts          | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts b/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
index 2b9011930e66f..dfe82c9e74ebd 100644
--- a/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
+++ b/src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts
@@ -296,7 +296,7 @@ namespace ts {
                         start: 0,
                         length: 0,
                         messageText: "Argument for '--lib' option must be: 'es5', 'es6', 'es2015', 'es7', 'es2016', 'es2017', 'es2018', 'esnext', 'dom', 'dom.iterable', 'webworker', " +
-                            "'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', " + 
+                            "'webworker.importscripts', 'scripthost', 'es2015.core', 'es2015.collection', 'es2015.generator', 'es2015.iterable', 'es2015.promise', 'es2015.proxy', " +
                             "'es2015.reflect', 'es2015.symbol', 'es2015.symbol.wellknown', 'es2016.array.include', 'es2017.object', 'es2017.sharedmemory', 'es2017.string', 'es2017.intl', " +
                             "'es2017.typedarrays', 'es2018.asynciterable', 'es2018.intl', 'es2018.promise', 'es2018.regexp', 'esnext.array', 'esnext.symbol', 'esnext.intl', 'esnext.bigint', " +
                             "'esnext.array', 'esnext.string', 'esnext.promise'.",

From 0e27ccbdb7528a02f834c8f9ca1c17c209f34024 Mon Sep 17 00:00:00 2001
From: Wenlu Wang <wenlwan@microsoft.com>
Date: Fri, 9 Jul 2021 14:12:13 +0800
Subject: [PATCH 9/9] Fix lib reference

---
 src/compiler/commandLineParser.ts | 1 -
 src/lib/esnext.array.d.ts         | 3 ++-
 src/lib/esnext.string.d.ts        | 2 ++
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 985791da82fb6..c4a089125dfb4 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -71,7 +71,6 @@ namespace ts {
         ["es2021.promise", "lib.es2021.promise.d.ts"],
         ["es2021.string", "lib.es2021.string.d.ts"],
         ["es2021.weakref", "lib.es2021.weakref.d.ts"],
-        ["es2021.string", "lib.es2021.string.d.ts"],
         ["esnext.symbol", "lib.es2019.symbol.d.ts"],
         ["esnext.asynciterable", "lib.es2018.asynciterable.d.ts"],
         ["esnext.intl", "lib.esnext.intl.d.ts"],
diff --git a/src/lib/esnext.array.d.ts b/src/lib/esnext.array.d.ts
index f0cde2963d80a..7098ba72865ef 100644
--- a/src/lib/esnext.array.d.ts
+++ b/src/lib/esnext.array.d.ts
@@ -1,3 +1,5 @@
+/// <reference lib="es2019.array" />
+
 interface Array<T> {
     /**
      * Access item by relative indexing.
@@ -6,7 +8,6 @@ interface Array<T> {
     at(index: number): T | undefined;
 }
 
-
 interface ReadonlyArray<T> {
     /**
      * Access item by relative indexing.
diff --git a/src/lib/esnext.string.d.ts b/src/lib/esnext.string.d.ts
index 7a398a35bf95f..570a8b617e4cd 100644
--- a/src/lib/esnext.string.d.ts
+++ b/src/lib/esnext.string.d.ts
@@ -1,3 +1,5 @@
+/// <reference lib="es2021.string" />
+
 interface String {
     /**
      * Access string by relative indexing.