RegExp.prototype.exec()

str

The string against which to match the regular expression.

If the match succeeds, the exec() method returns an array (with extra properties index, input, and if the d flag is set, indices; see below) and updates the lastIndex property of the regular expression object. The returned array has the matched text as the first item, and then one item for each parenthetical capture group of the matched text.

If the match fails, the exec() method returns null, and sets lastIndex to 0.

Consider the following example:

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

The following table shows the state of result after running this script:

The following table shows the state of re after running this script:

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:

let myRe = /ab*/g;
let str = 'abbcdefabh';
let myArray;
while ((myArray = myRe.exec(str)) !== null) {
  let 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

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

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

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

• Regular Expressions chapter in the JavaScript Guide
• RegExp