import
The static import
declaration is used to import read-only live bindings which are exported by another module.
Imported modules are in strict mode
whether you declare them as such or not. The import
statement cannot be
used in embedded scripts unless such script has a type="module"
. Bindings
imported are called live bindings because they are updated by the module that exported
the binding.
There is also a function-like dynamic import()
, which does not require scripts of type="module"
.
Backward compatibility can be ensured using attribute nomodule
on the
<script>
tag.
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 innode_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
The name
parameter is the name of the "module object" which will be used
as a kind of namespace to refer to the exports. The export
parameters
specify individual named exports, while the import * as name
syntax imports
all of them. Below are examples to clarify the syntax.
import
declarations are only permitted at the top-level of modules, and can only be present in module files. If an import
declaration is encountered in non-module contexts (for example, script files, eval
, new Function
, which all have "script" or "function" 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 top-level, all bindings must be identifiers...), which allows modules to be statically analyzed and synchronously linked before getting evaluated. This is the key to making modules asynchronous by nature, powering features like top-level await.
Import an entire module's contents
This inserts myModule
into the current scope, containing all the exports
from the module in the file located in /modules/my-module.js
.
import * as myModule from '/modules/my-module.js';
Here, accessing the exports means using the module name ("myModule" in this case) as a
namespace. For example, if the module imported above includes an export
doAllTheAmazingThings()
, you would call it like this:
myModule.doAllTheAmazingThings();
myModule
is an object with null
prototype, and the default export will be available as a key called default
.
Import a single export from a module
Given an object or value named myExport
which has been exported from the
module my-module
either implicitly (because the entire module is exported,
for example using export * from 'another.js'
) or explicitly (using the
export
statement), this inserts myExport
into the current scope.
import {myExport} from '/modules/my-module.js';
Import multiple exports from module
This inserts both foo
and bar
into the current scope.
import {foo, bar} from '/modules/my-module.js';
Import an export with a more convenient alias
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";
Rename multiple exports during import
Import multiple exports from a module with convenient aliases.
import {
reallyReallyLongModuleExportName as shortName,
anotherLongModuleName as short
} from '/modules/my-module.js';
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';
If your project uses packages that export ESM, you can also import them for side effects only. This will run the code in the package entry point file (and any files it imports) only.
Importing defaults
It is possible to have a default export
(whether it
is an object, a function, a class, etc.). The import
statement may then be
used to import such defaults.
The simplest version directly imports the default:
import myDefault from '/modules/my-module.js';
It is also possible to use the default syntax with the ones seen above (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 used as a namespace
or
import myDefault, {foo, bar} from '/modules/my-module.js';
// specific, named imports
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';
Examples
Standard Import
The code below shows how to import from a secondary module to assist in processing an AJAX JSON request.
The module: file.js
function getJSON(url, callback) {
let xhr = new XMLHttpRequest();
xhr.onload = function () {
callback(this.responseText)
};
xhr.open('GET', url, true);
xhr.send();
}
export function getUsefulContents(url, callback) {
getJSON(url, data => callback(JSON.parse(data)));
}
The main program: main.js
import { getUsefulContents } from '/modules/file.js';
getUsefulContents('http://www.example.com',
data => { doSomethingUseful(data); });
Specifications
Specification |
---|
ECMAScript Language Specification # sec-imports |
Browser compatibility
BCD tables only load in the browser
See also
export
- Dynamic imports
import.meta
- Limin Zhu, Brian Terlson and Microsoft Edge Team: Previewing ES6 Modules and more from ES2015, ES2016 and beyond
- Hacks blog post by Jason Orendorff: ES6 in Depth: Modules
- Hacks blog post by Lin Clark: ES modules: A cartoon deep-dive
- Axel Rauschmayer's book: "Exploring JS: Modules"
- The Modern JavaScript Tutorial(javascript.info): Export and Import