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RegExp.prototype.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.

Returns

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. [1] = Brown
[2] = Jumps
index The 0-based index of the match in the string. 4
input The original string. The Quick Brown Fox Jumps Over The Lazy Dog
re lastIndex The index at which to start the next match. When "g" is absent, this will remain as 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 in strings across multiple line. 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). 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 is set or a 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  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

See also