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); // "" 

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" 

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.

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