String.prototype.search()

Summary: in this tutorial, you’ll learn how to use the JavaScript String search() function to search for a match of a string with a regular expression and return the first match.

Introduction to the JavaScript String search() function #

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

let index = str.search(regexp);Copy

In this syntax, the regexp is a regular expression object.

If you pass a value that is not a RegExp object to the method, it will convert that value to a RegExp object using the following expression:

RegExp(regexp)Copy

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

Besides a regular expression object, you can pass any object that has Symbol.search() method to the search() method.

JavaScript String search() method examples #

Let’s take some examples of using the JavaScript search() function.

Basic JavaScript string search() method usages #

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

let re = /[A-Z]/;
let str = 'hi There! How are you?';
let index = str.search(re);

console.log(index);Copy

Output:

3Copy

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:

let re = /[0-9]/;
let str = 'Hello, JavaScript!';
let index = str.search(re);

console.log(index);Copy

Output:

-1Copy

Passing an object with the Symbol.search method #

The following example illustrates how to use the search() method with an object that has the Symbol.search method:

class EmailDomainChecker {
  constructor(domain) {
    this.domain = domain;
  }

  [Symbol.search](email) {
    if (!email.includes("@")) {
      return -1;
    }
    const [, domain] = email.split("@");
    return domain === this.domain ? 1 : -1;
  }
}

const js = new EmailDomainChecker("javascripttutorial.net");

let isJsEmail = "[email protected]".search(js) === 1;
console.log({ isJsEmail });

isJsEmail = "[email protected]".search(js) === 1;
console.log({ isJsEmail });Copy

Output:

{ isJsEmail: true }
{ isJsEmail: false }Copy

How it works.

First, define a class EmailDomainChecker with a Symbol.search method that returns 1 if the email has a domain that matches with a specified domain, or -1 otherwise.

class EmailDomainChecker {
  constructor(domain) {
    this.domain = domain;
  }

  [Symbol.search](email) {
    if (!email.includes("@")) {
      return -1;
    }
    const [, domain] = email.split("@");
    return domain === this.domain ? 1 : -1;
  }
}Copy

Second, create a new EmailDomainChecker object with the gmail.com domain:

const js = new EmailDomainChecker("javascripttutorial.net");Copy

Third, check if the email [email protected] comes from the javascripttutorial.net domain using the search() method:

let isJsEmail = "[email protected]".search(js) === 1;
console.log({ isJsEmail });Copy

The search() method will invoke the Symbol.search method of the js object that returns 1 in this case.

Finally, check if the [email protected] email belongs to the domain name javascripttutorial.net:

isJsEmail = "[email protected]".search(js) === 1;
console.log({ isJsEmail });Copy

It returns -1 in this case.

Summary #

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