JavaScript Anonymous Functions

Last Updated : 16 Jan, 2026

An anonymous function is a function without a name, mainly used for specific or short-term tasks, and is often assigned to variables or passed as arguments where reuse is not required.

  • It omits the function name and is defined using the function keyword or arrow syntax.
  • It is commonly used as callbacks or for one-time execution within a limited scope.
JavaScript 
let greet = function() {
  console.log("Hello!");
};
greet();

Syntax:

The below-enlightened syntax illustrates the declaration of an anonymous function using the normal declaration:

function() {    // Function Body }

We may also declare an anonymous function using the arrow function technique which is shown below:

( () => {    // Function Body...} )();

Note: You'll get a syntax error if you don't use parentheses (). The parentheses are needed to treat the anonymous function as an expression, which returns a function object.

[Example 1]: An anonymous function is defined to print a message, stored in the greet variable, and executed by calling greet().

JavaScript 
const greet = function () {
	console.log("Welcome to GeeksforGeeks!");
};
    
greet();

[Example 2] : Passing arguments to the anonymous function.

JavaScript 
const greet = function( str ) {
	console.log("Welcome to ", str);
};
    
greet("GeeksforGeeks!");

As JavaScript supports Higher-Order Functions, we can also pass anonymous functions as parameters into another function.

[Example 3]: Passing an anonymous function as a callback function to the setTimeout() method. This executes this anonymous function 2000ms later.

JavaScript 
setTimeout(function () {
	console.log("Welcome to GeeksforGeeks!");
}, 2000);

Self-Executing Anonymous Functions

Another common use of anonymous functions is to create self-executing functions (also known as IIFE - Immediately Invoked Function Expressions). These functions run immediately after they are defined.

[Example]: Creating a self-executing function.

JavaScript 
(function () {
	console.log("Welcome to GeeksforGeeks!");
})();

Arrow functions

Arrow Functions are a shorter ES6 syntax for writing anonymous functions, where the function keyword is not required and => is used to define the function.

  • They provide a more concise and readable syntax.
  • Commonly used for callbacks and short function expressions.

[Example 1] : This is an example of anonymous function with arrow function.

JavaScript 
const greet = () => {
	console.log("Welcome to GeeksforGeeks!");
}
    
greet();
  • If an arrow function has only one statement, curly braces {} can be omitted.
  • The result of that statement is returned automatically without using return.

[Example 2]: A simple arrow function with a single expression is used.

JavaScript 
const greet = () => console.log("Welcome to GeeksforGeeks!");

greet();

[Example 3]: lllustrates a self-executing function (IIFE), which immediately invokes itself after being defined

JavaScript 
(() => {
	console.log("GeeksforGeeks");
})();
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