esm: use import attributes instead of import assertions

The old import assertions proposal has been
renamed to "import attributes" with the follwing major changes:

1. The keyword is now `with` instead of `assert`.
2. Unknown assertions cause an error rather than being ignored,

This commit updates the documentation to encourage folks to use the new
syntax, and add aliases for module customization hooks.

PR-URL: nodejs#50140
Fixes: nodejs#50134
Refs: v8/v8@159c82c
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
Reviewed-By: Jacob Smith <jacob@frende.me>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

doc/api/errors.md

@@ -1759,7 +1759,8 @@ added:
   - v16.14.0
 -->
 
-An import assertion has failed, preventing the specified module to be imported.
+An import `type` attribute was provided, but the specified module is of a
+different type.
 
 <a id="ERR_IMPORT_ASSERTION_TYPE_MISSING"></a>
 
@@ -1771,7 +1772,7 @@ added:
   - v16.14.0
 -->
 
-An import assertion is missing, preventing the specified module to be imported.
+An import attribute is missing, preventing the specified module to be imported.
 
 <a id="ERR_IMPORT_ASSERTION_TYPE_UNSUPPORTED"></a>
 
@@ -1783,7 +1784,17 @@ added:
   - v16.14.0
 -->
 
-An import assertion is not supported by this version of Node.js.
+An import attribute is not supported by this version of Node.js.
+
+<a id="ERR_IMPORT_ATTRIBUTE_UNSUPPORTED"></a>
+
+### `ERR_IMPORT_ATTRIBUTE_UNSUPPORTED`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+An import attribute is not supported by this version of Node.js.
 
 <a id="ERR_INCOMPATIBLE_OPTION_PAIR"></a>
 

doc/api/esm.md

@@ -7,6 +7,9 @@
 <!-- YAML
 added: v8.5.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/50140
+    description: Add experimental support for import attributes.
   - version: v20.0.0
     pr-url: https://github.com/nodejs/node/pull/44710
     description: Module customization hooks are executed off the main thread.
@@ -19,7 +22,7 @@ changes:
     - v17.1.0
     - v16.14.0
     pr-url: https://github.com/nodejs/node/pull/40250
-    description: Add support for import assertions.
+    description: Add experimental support for import assertions.
   - version:
     - v17.0.0
     - v16.12.0
@@ -202,7 +205,7 @@ added: v12.10.0
 
 ```js
 import 'data:text/javascript,console.log("hello!");';
-import _ from 'data:application/json,"world!"' assert { type: 'json' };
+import _ from 'data:application/json,"world!"' with { type: 'json' };
 ```
 
 `data:` URLs only resolve [bare specifiers][Terminology] for builtin modules
@@ -234,30 +237,40 @@ absolute URL strings.
 import fs from 'node:fs/promises';
 ```
 
-## Import assertions
+<a id="import-assertions"></a>
+
+## Import attributes
 
 <!-- YAML
 added:
   - v17.1.0
   - v16.14.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/50140
+    description: Switch from Import Assertions to Import Attributes.
 -->
 
-> Stability: 1 - Experimental
+> Stability: 1.1 - Active development
+
+> This feature was previously named "Import assertions", and using the `assert`
+> keyword instead of `with`. Any uses in code of the prior `assert` keyword
+> should be updated to use `with` instead.
 
-The [Import Assertions proposal][] adds an inline syntax for module import
+The [Import Attributes proposal][] adds an inline syntax for module import
 statements to pass on more information alongside the module specifier.
 
 ```js
-import fooData from './foo.json' assert { type: 'json' };
+import fooData from './foo.json' with { type: 'json' };
 
 const { default: barData } =
-  await import('./bar.json', { assert: { type: 'json' } });
+  await import('./bar.json', { with: { type: 'json' } });
 ```
 
-Node.js supports the following `type` values, for which the assertion is
+Node.js supports the following `type` values, for which the attribute is
 mandatory:
 
-| Assertion `type` | Needed for       |
+| Attribute `type` | Needed for       |
 | ---------------- | ---------------- |
 | `'json'`         | [JSON modules][] |
 
@@ -544,10 +557,10 @@ separate cache.
 JSON files can be referenced by `import`:
 
 ```js
-import packageConfig from './package.json' assert { type: 'json' };
+import packageConfig from './package.json' with { type: 'json' };
 ```
 
-The `assert { type: 'json' }` syntax is mandatory; see [Import Assertions][].
+The `with { type: 'json' }` syntax is mandatory; see [Import Attributes][].
 
 The imported JSON only exposes a `default` export. There is no support for named
 exports. A cache entry is created in the CommonJS cache to avoid duplication.
@@ -1050,8 +1063,8 @@ resolution for ESM specifiers is [commonjs-extension-resolution-loader][].
 [Determining module system]: packages.md#determining-module-system
 [Dynamic `import()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import
 [ES Module Integration Proposal for WebAssembly]: https://github.com/webassembly/esm-integration
-[Import Assertions]: #import-assertions
-[Import Assertions proposal]: https://github.com/tc39/proposal-import-assertions
+[Import Attributes]: #import-attributes
+[Import Attributes proposal]: https://github.com/tc39/proposal-import-attributes
 [JSON modules]: #json-modules
 [Module customization hooks]: module.md#customization-hooks
 [Node.js Module Resolution And Loading Algorithm]: #resolution-algorithm-specification

doc/api/module.md

@@ -458,6 +458,11 @@ register('./path-to-my-hooks.js', {
 
 <!-- YAML
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/50140
+    description: The property `context.importAssertions` is replaced with
+                 `context.importAttributes`. Using the old name is still
+                 supported and will emit an experimental warning.
   - version:
     - v18.6.0
     - v16.17.0
@@ -477,8 +482,8 @@ changes:
 * `specifier` {string}
 * `context` {Object}
   * `conditions` {string\[]} Export conditions of the relevant `package.json`
-  * `importAssertions` {Object} An object whose key-value pairs represent the
-    assertions for the module to import
+  * `importAttributes` {Object} An object whose key-value pairs represent the
+    attributes for the module to import
   * `parentURL` {string|undefined} The module importing this one, or undefined
     if this is the Node.js entry point
 * `nextResolve` {Function} The subsequent `resolve` hook in the chain, or the
@@ -489,7 +494,7 @@ changes:
   * `format` {string|null|undefined} A hint to the load hook (it might be
     ignored)
     `'builtin' | 'commonjs' | 'json' | 'module' | 'wasm'`
-  * `importAssertions` {Object|undefined} The import assertions to use when
+  * `importAttributes` {Object|undefined} The import attributes to use when
     caching the module (optional; if excluded the input will be used)
   * `shortCircuit` {undefined|boolean} A signal that this hook intends to
     terminate the chain of `resolve` hooks. **Default:** `false`
@@ -506,10 +511,10 @@ the final `format` value (and it is free to ignore the hint provided by
 `resolve`); if `resolve` provides a `format`, a custom `load` hook is required
 even if only to pass the value to the Node.js default `load` hook.
 
-Import type assertions are part of the cache key for saving loaded modules into
+Import type attributes are part of the cache key for saving loaded modules into
 the internal module cache. The `resolve` hook is responsible for returning an
-`importAssertions` object if the module should be cached with different
-assertions than were present in the source code.
+`importAttributes` object if the module should be cached with different
+attributes than were present in the source code.
 
 The `conditions` property in `context` is an array of conditions for
 [package exports conditions][Conditional exports] that apply to this resolution
@@ -575,7 +580,7 @@ changes:
   * `conditions` {string\[]} Export conditions of the relevant `package.json`
   * `format` {string|null|undefined} The format optionally supplied by the
     `resolve` hook chain
-  * `importAssertions` {Object}
+  * `importAttributes` {Object}
 * `nextLoad` {Function} The subsequent `load` hook in the chain, or the
   Node.js default `load` hook after the last user-supplied `load` hook
   * `specifier` {string}

lib/internal/errors.js

@@ -1178,12 +1178,17 @@ E('ERR_HTTP_SOCKET_ENCODING',
 E('ERR_HTTP_TRAILER_INVALID',
   'Trailers are invalid with this transfer encoding', Error);
 E('ERR_ILLEGAL_CONSTRUCTOR', 'Illegal constructor', TypeError);
+// TODO(aduh95): change the error to mention import attributes instead of import assertions.
 E('ERR_IMPORT_ASSERTION_TYPE_FAILED',
   'Module "%s" is not of type "%s"', TypeError);
+// TODO(aduh95): change the error to mention import attributes instead of import assertions.
 E('ERR_IMPORT_ASSERTION_TYPE_MISSING',
-  'Module "%s" needs an import assertion of type "%s"', TypeError);
+  'Module "%s" needs an import attribute of type "%s"', TypeError);
+// TODO(aduh95): change the error to mention import attributes instead of import assertions.
 E('ERR_IMPORT_ASSERTION_TYPE_UNSUPPORTED',
-  'Import assertion type "%s" is unsupported', TypeError);
+  'Import attribute type "%s" is unsupported', TypeError);
+E('ERR_IMPORT_ATTRIBUTE_UNSUPPORTED',
+  'Import attribute "%s" with value "%s" is not supported', TypeError);
 E('ERR_INCOMPATIBLE_OPTION_PAIR',
   'Option "%s" cannot be used in combination with option "%s"', TypeError);
 E('ERR_INPUT_TYPE_NOT_ALLOWED', '--input-type can only be used with string ' +

lib/internal/modules/cjs/loader.js

@@ -1295,10 +1295,10 @@ function wrapSafe(filename, content, cjsModuleInstance, codeCache) {
     const script = new Script(wrapper, {
       filename,
       lineOffset: 0,
-      importModuleDynamically: async (specifier, _, importAssertions) => {
+      importModuleDynamically: async (specifier, _, importAttributes) => {
         const cascadedLoader = getCascadedLoader();
         return cascadedLoader.import(specifier, normalizeReferrerURL(filename),
-                                     importAssertions);
+                                     importAttributes);
       },
     });
 
@@ -1322,10 +1322,10 @@ function wrapSafe(filename, content, cjsModuleInstance, codeCache) {
     ], {
       filename,
       cachedData: codeCache,
-      importModuleDynamically(specifier, _, importAssertions) {
+      importModuleDynamically(specifier, _, importAttributes) {
         const cascadedLoader = getCascadedLoader();
         return cascadedLoader.import(specifier, normalizeReferrerURL(filename),
-                                     importAssertions);
+                                     importAttributes);
       },
     });
 

lib/internal/modules/esm/assert.js

@@ -13,16 +13,15 @@ const {
   ERR_IMPORT_ASSERTION_TYPE_FAILED,
   ERR_IMPORT_ASSERTION_TYPE_MISSING,
   ERR_IMPORT_ASSERTION_TYPE_UNSUPPORTED,
+  ERR_IMPORT_ATTRIBUTE_UNSUPPORTED,
 } = require('internal/errors').codes;
 
 // The HTML spec has an implied default type of `'javascript'`.
 const kImplicitAssertType = 'javascript';
 
-let alreadyWarned = false;
-
 /**
- * Define a map of module formats to import assertion types (the value of
- * `type` in `assert { type: 'json' }`).
+ * Define a map of module formats to import attributes types (the value of
+ * `type` in `with { type: 'json' }`).
  * @type {Map<string, string>}
  */
 const formatTypeMap = {
@@ -31,13 +30,13 @@ const formatTypeMap = {
   'commonjs': kImplicitAssertType,
   'json': 'json',
   'module': kImplicitAssertType,
-  'wasm': kImplicitAssertType, // It's unclear whether the HTML spec will require an assertion type or not for Wasm; see https://github.com/WebAssembly/esm-integration/issues/42
+  'wasm': kImplicitAssertType, // It's unclear whether the HTML spec will require an attribute type or not for Wasm; see https://github.com/WebAssembly/esm-integration/issues/42
 };
 
 /**
  * The HTML spec disallows the default type to be explicitly specified
  * (for now); so `import './file.js'` is okay but
- * `import './file.js' assert { type: 'javascript' }` throws.
+ * `import './file.js' with { type: 'javascript' }` throws.
  * @type {Array<string, string>}
  */
 const supportedAssertionTypes = ArrayPrototypeFilter(
@@ -46,54 +45,50 @@ const supportedAssertionTypes = ArrayPrototypeFilter(
 
 
 /**
- * Test a module's import assertions.
+ * Test a module's import attributes.
  * @param {string} url The URL of the imported module, for error reporting.
  * @param {string} format One of Node's supported translators
- * @param {Record<string, string>} importAssertions Validations for the
+ * @param {Record<string, string>} importAttributes Validations for the
  *                                                  module import.
  * @returns {true}
  * @throws {TypeError} If the format and assertion type are incompatible.
  */
-function validateAssertions(url, format,
-                            importAssertions = { __proto__: null }) {
-  const validType = formatTypeMap[format];
-
-  if (!alreadyWarned && ObjectKeys(importAssertions).length !== 0) {
-    alreadyWarned = true;
-    process.emitWarning(
-      'Import assertions are not a stable feature of the JavaScript language. ' +
-      'Avoid relying on their current behavior and syntax as those might change ' +
-      'in a future version of Node.js.',
-      'ExperimentalWarning',
-    );
+function validateAttributes(url, format,
+                            importAttributes = { __proto__: null }) {
+  const keys = ObjectKeys(importAttributes);
+  for (let i = 0; i < keys.length; i++) {
+    if (keys[i] !== 'type') {
+      throw new ERR_IMPORT_ATTRIBUTE_UNSUPPORTED(keys[i], importAttributes[keys[i]]);
+    }
   }
+  const validType = formatTypeMap[format];
 
   switch (validType) {
     case undefined:
-      // Ignore assertions for module formats we don't recognize, to allow new
+      // Ignore attributes for module formats we don't recognize, to allow new
       // formats in the future.
       return true;
 
     case kImplicitAssertType:
       // This format doesn't allow an import assertion type, so the property
-      // must not be set on the import assertions object.
-      if (!ObjectPrototypeHasOwnProperty(importAssertions, 'type')) {
+      // must not be set on the import attributes object.
+      if (!ObjectPrototypeHasOwnProperty(importAttributes, 'type')) {
         return true;
       }
-      return handleInvalidType(url, importAssertions.type);
+      return handleInvalidType(url, importAttributes.type);
 
-    case importAssertions.type:
+    case importAttributes.type:
       // The asserted type is the valid type for this format.
       return true;
 
     default:
       // There is an expected type for this format, but the value of
-      // `importAssertions.type` might not have been it.
-      if (!ObjectPrototypeHasOwnProperty(importAssertions, 'type')) {
+      // `importAttributes.type` might not have been it.
+      if (!ObjectPrototypeHasOwnProperty(importAttributes, 'type')) {
         // `type` wasn't specified at all.
         throw new ERR_IMPORT_ASSERTION_TYPE_MISSING(url, validType);
       }
-      return handleInvalidType(url, importAssertions.type);
+      return handleInvalidType(url, importAttributes.type);
   }
 }
 
@@ -118,5 +113,5 @@ function handleInvalidType(url, type) {
 
 module.exports = {
   kImplicitAssertType,
-  validateAssertions,
+  validateAttributes,
 };