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));

Output:

is

Example: JavaScript substr method

const answer = 42;

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

Output:

test

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.