Global / Window

`atob`

Decodes a string of data which has been encoded using Base64 encoding

Syntax

JavaScript

atob(encodedData)

Parameters

Parameter	Type	Description
encodedData	string	A binary string containing base64-encoded data

Return Value

A string containing decoded data from encodedData

Examples

Basic Usage

const decoded = atob('SGVsbG8gV29ybGQ=');
console.log(decoded); // 'Hello World'

Practical Example

const base64 = 'eyJuYW1lIjoiQWxpY2UifQ==';
const json = atob(base64);
console.log(JSON.parse(json)); // { name: 'Alice' }

Advanced Usage

function decodeJwtPayload(token: string) {
  const payload = token.split('.')[1];
  return JSON.parse(atob(payload));
}

Understanding atob

The atob method in JavaScript decodes a string of data which has been encoded using Base64 encoding. It belongs to the window object and is one of the most widely used methods for working with window values in modern JavaScript and TypeScript applications.

The method signature is atob(encodedData). It accepts 1 parameter: encodedData. When called, it returns a string containing decoded data from encodeddata. Understanding when and how to use atob() helps you write more expressive, readable code.

Common use cases for atob include data transformation, input validation, API response processing, and building reusable utility functions. It works well alongside related methods like window-btoa, enabling you to chain operations together for complex data manipulation pipelines.

Browser support for atob is excellent across all modern browsers including Chrome, Firefox, Safari, and Edge. It is also fully supported in Node.js and Deno. For older environments, transpilation with Babel or a polyfill may be needed.