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import

The static import declaration is used to import read-only live bindings which are exported by another module. The imported bindings are called live bindings because they are updated by the module that exported the binding, but cannot be modified by the importing module.

In order to use the import declaration in a source file, the file must be interpreted by the runtime as a module. In HTML, this is done by adding type="module" to the <script> tag. Modules are automatically interpreted in strict mode.

There is also a function-like dynamic import(), which does not require scripts of type="module".

Syntax

import defaultExport from "module-name";
import * as name from "module-name";
import { export1 } from "module-name";
import { export1 as alias1 } from "module-name";
import { default as alias } from "module-name";
import { export1, export2 } from "module-name";
import { export1, export2 as alias2, /* … */ } from "module-name";
import { "string name" as alias } from "module-name";
import defaultExport, { export1, /* … */ } from "module-name";
import defaultExport, * as name from "module-name";
import "module-name";
defaultExport

Name that will refer to the default export from the module. Must be a valid JavaScript identifier.

module-name

The module to import from. The evaluation of the specifier is host-specified. This is often a relative or absolute URL to the .js file containing the module. In Node, extension-less imports often refer to packages in node_modules. Certain bundlers may permit importing files without extensions; check your environment. Only single quoted and double quoted Strings are allowed.

name

Name of the module object that will be used as a kind of namespace when referring to the imports. Must be a valid JavaScript identifier.

exportN

Name of the exports to be imported. The name can be either an identifier or a string literal, depending on what module-name declares to export. If it is a string literal, it must be aliased to a valid identifier.

aliasN

Names that will refer to the named imports. Must be a valid JavaScript identifier.

Description

import declarations can only be present in modules, and only at the top-level (i.e. not inside blocks, functions, etc.). If an import declaration is encountered in non-module contexts (for example, <script> tags without type="module", eval, new Function, which all have "script" or "function body" as parsing goals), a SyntaxError is thrown. To load modules in non-module contexts, use the dynamic import syntax instead.

import declarations are designed to be syntactically rigid (for example, only string literal specifiers, only permitted at the top-level, all bindings must be identifiers), which allows modules to be statically analyzed and linked before getting evaluated. This is the key to making modules asynchronous by nature, powering features like top-level await.

There are four forms of import declarations:

Below are examples to clarify the syntax.

Named import

Given a value named myExport which has been exported from the module my-module either implicitly as export * from 'another.js') or explicitly using the export statement, this inserts myExport into the current scope.

import { myExport } from '/modules/my-module.js';

You can import multiple names from the same module.

import { foo, bar } from '/modules/my-module.js';

You can rename an export when importing it. For example, this inserts shortName into the current scope.

import {
  reallyReallyLongModuleExportName as shortName,
} from '/modules/my-module.js';

A module may also export a member as a string literal which is not a valid identifier, in which case you must alias it in order to use it in the current module.

// /modules/my-module.js
const a = 1;
export { a as "a-b" };
import { "a-b" as a } from "/modules/my-module.js";

Note: import { x, y } from "mod" is not equivalent to import defaultExport from "mod" and then destructuring x and y from defaultExport. Named and default imports are distinct syntaxes in JavaScript modules.

Default import

Default exports need to be imported with the corresponding default import syntax. The simplest version directly imports the default:

import myDefault from '/modules/my-module.js';

Since the default export doesn't explicitly specify a name, you can give the identifier any name you like.

It is also possible to specify a default import with namespace imports or named imports. In such cases, the default import will have to be declared first. For instance:

import myDefault, * as myModule from '/modules/my-module.js';
// myModule.default and myDefault point to the same binding

or

import myDefault, { foo, bar } from '/modules/my-module.js';

Importing a name called default has the same effect as a default import. It is necessary to alias the name because default is a reserved word.

import { default as myDefault } from '/modules/my-module.js';

Namespace import

The following code inserts myModule into the current scope, containing all the exports from the module located at /modules/my-module.js.

import * as myModule from '/modules/my-module.js';

Here, myModule represents a namespace object which contains all exports as properties. For example, if the module imported above includes an export doAllTheAmazingThings(), you would call it like this:

myModule.doAllTheAmazingThings();

myModule is a sealed object with null prototype. All keys are enumerable in lexicographic order (i.e. the default behavior of Array.prototype.sort()), with the default export available as a key called default.

Note: JavaScript does not have wildcard imports like import * from "module-name", because of the high possibility of name conflicts.

Import a module for its side effects only

Import an entire module for side effects only, without importing anything. This runs the module's global code, but doesn't actually import any values.

import '/modules/my-module.js';

This is often used for polyfills, which mutate the global variables.

Examples

Standard Import

In this example, we create a re-usable module that exports a function to get all primes within a given range.

// getPrimes.js
/**
 * Returns a list of prime numbers that are smaller than `max`.
 */
function getPrimes(max) {
  const isPrime = Array.from({ length: max }, () => true);
  isPrime[0] = isPrime[1] = false;
  isPrime[2] = true;
  for (let i = 2; i * i < max; i++) {
    if (isPrime[i]) {
      for (let j = i ** 2; j < max; j += i) {
        isPrime[j] = false;
      }
    }
  }
  return [...isPrime.entries()]
    .filter(([, isPrime]) => isPrime)
    .map(([number]) => number);
}
import { getPrimes } from '/modules/getPrimes.js';

console.log(getPrimes(10)); // [2, 3, 5, 7]

Imported values can only be modified by the exporter

The identifier being imported is a live binding, because the module exporting it may mutate it and the imported value would change. However, the module importing it cannot re-assign it.

// my-module.js
export let myValue = 1;
setTimeout(() => {
  myValue = 2;
}, 500);
// main.js
import { myValue } from '/modules/my-module.js';
console.log(myValue); // 1
setTimeout(() => {
  console.log(myValue); // 2; my-module has updated its value
  myValue = 3; // TypeError: Assignment to constant variable.
  // The importing module can only read the value but can't re-assign it.
}, 1000);

Specifications

Browser compatibility

Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet Deno Node.js
import
61
16
60
No
48
10.1
61
61
60
45
10.3
8.0
1.0
13.2.0
Modules must either have a filename ending in .mjs, or the nearest parent package.json file must contain "type": "module". See Node's ECMAScript Modules documentation for more details.
12.0.0-13.2.0
Modules must either have a filename ending in .mjs, or the nearest parent package.json file must contain "type": "module". See Node's ECMAScript Modules documentation for more details.
8.5.0-12.0.0
Module filenames must end with .mjs, not .js. See Node's ECMAScript Modules documentation for more details.
worker_support
80
80
No
No
No
15
80
80
No
No
15
13.0
1.0
No

See also

© 2005–2022 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import