JavaScript String substr() Tutorial

In this section, we will learn what the substr() method is and how to use it.

JavaScript String substr() Method

The string substr() method is used to extract a sub-string from another string value.

Note: this method won’t change the original text content.

JavaScript String substr() Syntax

string.substr(start, length)

String substr() Method Parameters:

The method takes two arguments:

  • The first argument is the index number from which the extraction should start.

Note: if the value is negative, that means start from the last character of the string value and count backward to declare the start index position.

Note: the first character in a string value starts from the index number 0.

  • The second argument is the number of characters that we want to extract. This value is optional and if ignored, that means all the characters from the start-index to the end of the string value.

Note: if we use a negative number as the second argument, it will be treated as 0. So the final result will be an empty string.

String substr() Method Return Value:

The return value of this method is a new sub-string value that was extracted from the original text content.

Example: using substr() method in JavaScript

console.log("This is for test".substr(5,2));



Example: JavaScript substr method

const answer = 42;

console.log("This is for test".substr(-4,4));



Because we used the negative number as the first argument, the starting position is declared from the end of the string towards the beginning. The value here is -4, so then count 4 characters backwards from the end of the string-value and that will be the starting position of the extraction.

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