Regular Expressions (Javascript)

In Javascript, regular expressions are enclosed within two forward slashes and flags are placed oustide.

let re = /hello/m;  // or
let re = new RegExp('hello', 'm');


.exec() / .match()

re.exec(item) and item.match(re) will search for the regex (re) inside of item. If found, this returns the expression, the index of beginning of match, and the input item. if not found, this returns null.


item.replace(re, replacement) will replace instances of regex (re) with replacement and return the modified item.

.search() returns index of first found instance of reg ex in item. if not found, returns -1.


re.source returns the reg expression without the slashes, re being a variable holding a regular expression.

let re = /hello/m;
console.log(re.source); // "hello"


item.split(re) returns an array of the string split by the regex.

var myString = 'Hello 1 word. Sentence number 2.';
var splits = myString.split(/(\d)/);
// returns [ "Hello ", "1", " word. Sentence number ", "2", "." ]


re.test(item) returns boolean of if regex is found in item.

let re = /hello/m;
re.test('hello world!') // returns true
re.test('me first') // returns false



Last modified: 202107020550