How to find the substring in javascript

Learn how to find the substring from a given string in javascript. We will use different methods to find the substrings.

Using slice()

slice() methods returns a part of the string as a substring without affecting the original string.

let str = 'I am Prashant Yadav';
let substring = str.slice(5);
console.log(substring);
//"Prashant Yadav"

It has extracted substring starting at index 5 till the end of the string.

The slice() methods takes two parameters as input.

String.slice(startIndex, endIndex)

startIndex

• Required. Zero-based index at which substring should start from.
• If negative number is provided then it will treated as stringLength + startIndex where stringLength is the length of the string. Like stringLength + (-3).
• If the startIndex is greater than or equal to the strings length then an empty substring will be returned.

endIndex

• Optional. Zero-based index before which to end extraction of the substring.
• If negative number is provided then it will treated as stringLength + endIndex where stringLength is the length of the string. Like stringLength + (-3).
• If endIndex is not provided the substring till the end of the string is returned.

let str = 'I am Prashant Yadav';

//With endIndex
let substring = str.slice(5, 8);
console.log(substring);
//Pra

//With negative startIndex
let substring = str.slice(-5);
console.log(substring);
//"Yadav"

//With negative endIndex
let substring = str.slice(5, -4);
console.log(substring);
//"Prashant Y"

//With startIndex > string length
let substring = str.slice(15, -4);
console.log(substring);
// ""

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Using substring()

substring() methods removes and return the new substring from a given string between the two specified indexes or to the end of the string.

let str = 'I am Prashant Yadav';
let substring = str.substring(5);
console.log(substring);
//"Prashant Yadav"

Returns all the characters starting at index 5 till end of the given string. It takes two parameters as input.

String.substring(startIndex, endIndex)

startIndex

• Required. Zero-based index from where the substring extraction should start.

endIndex

• Optional. Zero-based index before which substring extraction should end.
• The endIndex character is not included in the string.
• If omitted it will return all the characters till the end of the string.

let str = 'I am Prashant Yadav';
let substring = str.substring(5, 10);
console.log(substring);
//"Prash"

There are few things you should keep note of while using substring()

• If startIndex and endIndex are equal then it will return empty substring.
• If startIndex is greater than endIndex then it will swap the indexes and return the substring accordingly. Like str.substring(10, 5) will be swapped to str.substring(5, 10)

let str = 'I am Prashant Yadav';

//When startIndex and endIndex are same
let substring = str.substring(5, 5);
console.log(substring);
// ""

//When startIndex > endIndex
let substring = str.substring(10, 5);
console.log(substring);
//"Prash"

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Difference between substring() and slice()

Both methods may seem to do the same work but there is a subtle difference in them.

• If the startIndex is greater than endIndex. substring() will swap the two indexes, while slice() will return an empty substring.
• If any one or both the indexes are given negative or NaN. substring() will treat them as 0. While slice() treats NaN as 0 but for the negative values it starts the count from the end of the string.

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You can also use substr method. But it is going to be deprecated in the future so its better to avoid it.