W3cubDocs

regExp.exec

The exec() method executes a search for a match in a specified string. Returns a result array, or null.

If you are executing a match simply to find true or false, use the RegExp.prototype.test() method or the String.prototype.search() method.

Syntax

regexObj.exec(str)

Parameters

str: The string against which to match the regular expression.

Return value

If the match succeeds, the exec() method returns an array and updates properties of the regular expression object. The returned array has the matched text as the first item, and then one item for each capturing parenthesis that matched containing the text that was captured.

If the match fails, the exec() method returns null.

Description

Consider the following example:

// Match "quick brown" followed by "jumps", ignoring characters in between
// Remember "brown" and "jumps"
// Ignore case
var re = /quick\s(brown).+?(jumps)/ig;
var result = re.exec('The Quick Brown Fox Jumps Over The Lazy Dog');

The following table shows the results for this script:

Object	Property/Index	Description	Example
`result`	`[0]`	The full string of characters matched	`"Quick Brown Fox Jumps"`
	`[1], ...[n]`	The parenthesized substring matches, if any. The number of possible parenthesized substrings is unlimited.	`result[1] === "Brown" result[2] === "Jumps"`
	`index`	The 0-based index of the match in the string.	`4`
	`input`	The original string that was matched against.	`"The Quick Brown Fox Jumps Over The Lazy Dog"`
`re`	`lastIndex`	The index at which to start the next match. If `g` is absent, this will always be `0`.	`25`
	`ignoreCase`	Indicates if the `i` flag was used to ignore case.	`true`
	`global`	Indicates if the `g` flag was used for a global match.	`true`
	`multiline`	Indicates if the `m` flag was used to search across multiple lines.	`false`
	`source`	The text of the pattern.	`"quick\s(brown).+?(jumps)"`

Examples

Finding successive matches

If your regular expression uses the "g" flag, you can use the exec() method multiple times to find successive matches in the same string. When you do so, the search starts at the substring of str specified by the regular expression's lastIndex property (test() will also advance the lastIndex property). Note that the lastIndex property will not be reset when searching a different string it will start its search at its existing lastIndex .

For example, assume you have this script:

var myRe = /ab*/g;
var str = 'abbcdefabh';
var myArray;
while ((myArray = myRe.exec(str)) !== null) {
  var msg = 'Found ' + myArray[0] + '. ';
  msg += 'Next match starts at ' + myRe.lastIndex;
  console.log(msg);
}

This script displays the following text:

Found abb. Next match starts at 3
Found ab. Next match starts at 9

Note: Do not place the regular expression literal (or RegExp constructor) within the while condition or it will create an infinite loop if there is a match due to the lastIndex property being reset upon each iteration. Also be sure that the global flag ("g") is set or an infinite loop will occur here also.

Using `exec()` with `RegExp` literals

You can also use exec() without creating a RegExp object:

var matches = /(hello \S+)/.exec('This is a hello world!');
console.log(matches[1]);

This will log a message containing 'hello world!'.

Specifications

Specification	Status	Comment
ECMAScript 3rd Edition (ECMA-262)	Standard	Initial definition. Implemented in JavaScript 1.2.
ECMAScript 5.1 (ECMA-262) The definition of 'RegExp.exec' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'RegExp.exec' in that specification.	Standard
ECMAScript Latest Draft (ECMA-262) The definition of 'RegExp.exec' in that specification.	Draft

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	Yes	Yes	1	Yes	Yes	Yes

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	Yes	Yes	Yes	4	Yes	Yes	Yes

	Server
	Node.js
Basic support	Yes