JavaScript Substring

The .substring() method in JavaScript extracts a portion of a string from one position to another (exclusive) and returns a new string. If the second position is omitted, it returns characters from the first position to the end of the string.

Syntax

string.substring(startIndex, endIndex);

Parameters:

• startIndex: The position where extraction begins.
• endIndex (Optional): The position before which to end extraction. If omitted, .substring() returns characters from startIndex to the end of the string.

Return value:

The .substring() method returns a newly created string containing the substring extracted from the input string.

Notes:

• If startIndex and endIndex are equal, .substring() returns an empty string.
• Indices that are greater than string.length are treated as string.length.
• If startIndex is greater than endIndex, then startIndex is treated as the end index and endIndex is treated as the start index.

Example 1: Basic Usage of .substring()

This example uses the .substring() method to extract characters from index 0 to index 4 (exclusive) in the str string:

let str = 'JavaScript';

let result = str.substring(0, 4);

console.log(result);

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Here is the output:

Java

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Example 2: Using .substring() Without endIndex

This example uses the .substring() method without the endIndex parameter to extract characters from index 9 to the end of the str string:

let str = 'Frontend Developer';

let result = str.substring(9);

console.log(result);

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Here is the output:

Developer

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Codebyte Example: Using .substring() with Reversed Indices

This codebyte example uses the .substring() method with the startIndex parameter being greater than endIndex to extract characters from index 0 to index 6 in the str string:

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Frequently Asked Questions

1. What happens if startIndex or endIndex in .substring() is negative?

If startIndex or endIndex in .substring() is negative, it is treated as 0.

2. How is .substring() different from .slice()?

• .substring() swaps the indices if the first is greater than the second, unlike .slice().
• .slice() supports negative indices, unlike .substring().

3. Can I use .substring() on string literals?

Yes, you can use .substring() on string literals because JavaScript treats them as temporary String objects, making them eligible for calling methods on.