JavaScript IIFE

Written by Swapnil RajaPublished 24 Aug 2026

A JavaScript IIFE is a function that runs immediately after it is defined.

IIFE stands for Immediately Invoked Function Expression.

It is written inside brackets and called straight away with a second pair of brackets.

Example

javascript

(function () {
  console.log("This runs at once");
})();

The function is defined and called on the same line.

It has no name, so nothing else can call it again.

What is an IIFE?

An IIFE is a function expression that calls itself as soon as it is created.

The outer brackets turn the function into an expression, and the final () runs it.

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Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript IIFE</title>
</head>
<body>

  <h1>JavaScript IIFE</h1>

  <p id="result"></p>

  <script>
    const app = (function () {
      const name = "My App";
      const version = "1.0";

      return {
        title: name + " v" + version
      };
    })();

    document.getElementById("result").innerHTML = app.title;
  </script>

</body>
</html>

JavaScript IIFE

Example

What is an IIFE?

Syntax

Keeping Variables Private

Example

An IIFE with Parameters

Example

Returning a Value

Example

The Arrow Function Form

Example

Do You Still Need One?

Example

Complete Example

Try It Yourself

Important Points

Conclusion