JavaScript Modules Tutorial

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JavaScript Modules Tutorial - HTML5ANDCSS3

JavaScript Modules

Written by Swapnil RajaPublished 24 Aug 2026

A module is a file that can export values for other files to import.

Before modules, every script shared one global scope, and names easily collided.

A module has its own scope; nothing is visible outside it unless exported.

Example

javascript

// The examples below simulate two files with a plain object,
// since import/export only works between real separate files.
const mathUtils = {
  double(n) {
    return n * 2;
  }
};

console.log(mathUtils.double(5));

PreviousJavaScript navigator Object NextJavaScript export

Example

javascript

const mathUtils = (function () {
  const secretHelper = 2;
  return {
    double: function (n) {
      return n * secretHelper;
    }
  };
})();

console.log(mathUtils.double(5));
console.log(typeof mathUtils.secretHelper);

Example

javascript

let runCount = 0;

function loadModule() {
  runCount++;
  return { value: 42 };
}

const first = loadModule();
const second = first;

console.log(runCount);
console.log(first === second);

Example

javascript

function strictAssign() {
  "use strict";
  let message;
  try {
    undeclaredName = 5;
  } catch (error) {
    message = error.name;
  }
  return message;
}

console.log(strictAssign());

Complete Example

html

<!-- /samples/math.js -->
<script type="module">
  export function double(n) {
    return n * 2;
  }
</script>

<!-- main.js, loaded as a module -->
<script type="module">
  import { double } from "/samples/math.js";

  document.getElementById("out").textContent = double(5);
</script>

<!-- In the HTML: -->
<!-- <script type="module" src="main.js"></script> -->

<p id="out"></p>

JavaScript Modules

Example

Why Modules Exist

Syntax

The Old Way

Example

A Module's Scope Is Private

Example

Only Exported Names Are Visible

Example

Modules Run Once

Example

Modules Are Strict by Default

Example

Complete Example

Try It Yourself

Important Points

Conclusion