Summary: in this tutorial, you’ll learn how to use the JavaScript String search() function to locate a substring within a string using a regular expression.

Introduction to the JavaScript String search() function

The search() method accepts a regular expression and returns the index of the first match in a string:

Code language: JavaScript (javascript)

In this syntax, the regexp is a regular expression. If you pass a non-RegExp into the method, it will convert that value to a RegExp.

If the search() doesn’t find any match, it returns -1.

JavaScript String search() method examples

The following example uses the search() method to return the first occurrence of any capital letter:

Code language: JavaScript (javascript)

Output:

Code language: JavaScript (javascript)

It returns 3 which is the index of the capital letter T.

The following example returns -1 because there is no number in the string:

Code language: JavaScript (javascript)

Output:

Code language: JavaScript (javascript)

Summary

• Use the JavaScript String search() to find the index of the first match based on a regular expression in a string.