String

`String.prototype.substring`

Returns the part of the string from the start index up to and excluding the end index

Syntax

JavaScript

string.substring(indexStart, indexEnd?)

Parameters

Parameter	Type	Description
indexStart	number	Index of the first character to include
indexEnd	number	Index of the first character to exclude

Return Value

A new string containing the specified part

Examples

Basic Usage

const str = 'JavaScript';
console.log(str.substring(0, 4)); // 'Java'
console.log(str.substring(4)); // 'Script'

Practical Example

const str = 'Hello World';
console.log(str.substring(6, 11)); // 'World'

Advanced Usage

// substring swaps arguments if start > end
const str = 'abcde';
console.log(str.substring(3, 1)); // 'bc' (same as substring(1, 3))

Understanding String.prototype.substring

The String.prototype.substring method in JavaScript returns the part of the string from the start index up to and excluding the end index. It belongs to the String object and is one of the most widely used methods for working with string values in modern JavaScript and TypeScript applications.

The method signature is string.substring(indexStart, indexEnd?). It accepts 2 parameters: indexStart, indexEnd. When called, it returns a new string containing the specified part. Understanding when and how to use substring() helps you write more expressive, readable code.

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

Browser support for String.prototype.substring 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.