JavaScript RegExp exec() Method

The RegExp.exec() method in JavaScript allows you to search for a pattern in a string and retrieve detailed information about the match. Unlike simple methods like test(), exec() returns not just a boolean, but an array containing the entire match, capturing groups, the position of the match, and more.

let regex = /(\d{2})-(\d{2})-(\d{4})/;
let s = "Today's date is 12-09-2023.";

let res = regex.exec(s);

if (res) {
    console.log("Full match:", res[0]);
    console.log("Day:", res[1]);
    console.log("Month:", res[2]);
    console.log("Year:", res[3]);
} else {
    console.log("No match found.");
}

Full match: 12-09-2023
Day: 12
Month: 09
Year: 2023

• Regular Expression: /(\d{2})-(\d{2})-(\d{4})/ matches a date in the format dd-mm-yyyy. The parentheses () are used to capture groups.
• exec() method: Searches the string for the pattern and returns an array with detailed match information:
• res[0]: The full matched string.
• res[1], res[2], res[3]: The captured groups (day, month, and year).
• If no match is found, exec() returns null.

Syntax:

let result = regex.exec(string);

• regex: The regular expression to search for in the string.
• string: The string to search within.
• result: An array of match details if a match is found, or null if no match is found.

Now let's see some uses of RegExp exec() Method

1. Extracting Email Components

Let’s use exec() to extract the domain from an email address:

let regex = /@([a-zA-Z0-9.-]+)/;
let mail = "user@example.com";

let res = regex.exec(mail);

if (res) {
    console.log("Domain:", res[1]);
} else {
    console.log("No domain found.");
}

Domain: example.com

2. Finding All Digits in a String

You can use exec() with the global flag (g) to find all occurrences of digits in a string

let regex = /\d+/g;
let s = "I have 2 apples and 15 bananas.";

let res;
while ((res = regex.exec(s)) !== null) {
    console.log("Found:", res[0], "at position:", res.index);
}

Found: 2 at position: 7
Found: 15 at position: 20

Key Points About exec()

• Detailed Match Information: exec() provides detailed information about the match, including the matched string, capture groups, the match's index in the input string, and the original input.
• Global Flag (g): When used with the g flag, exec() can find all matches in the string, returning results in a loop.
• Returns null on No Match: If no match is found, exec() returns null.