import

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.

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.

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.

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';

This inserts both foo and bar into the current scope.

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";

Import multiple exports from a module with convenient aliases.

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

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.

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';

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); });

• 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