JAVASCRIPT

Regex match word js

let string = "Hello world"; // you can use .toLowerCase() to check only in lower

let match = "world"; // word to match

let regex = new RegExp('('+match+')');

console.log('true for no match, false for match');
console.log(string.match(regex) == null); //.match() returns array of words found

// true for no match, false for match
// false

javascript regex example match

//Declare Reg using slash
let reg = /abc/
//Declare using class, useful for buil a RegExp from a variable
reg = new RegExp('abc')

//Option you must know: i -> Not case sensitive, g -> match all the string
let str = 'Abc abc abc'
str.match(/abc/) //Array(1) ["abc"] match only the first and return
str.match(/abc/g) //Array(2) ["abc","abc"] match all
str.match(/abc/i) //Array(1) ["Abc"] not case sensitive
str.match(/abc/ig) //Array(3) ["Abc","abc","abc"]
//the equivalent with new RegExp is
str.match('abc', 'ig') //Array(3) ["Abc","abc","abc"]

javascript regex exact match

var r = /^a$/

function matchExact(r, str) {
   var match = str.match(r);
   return match && str === match[0];
}

how to use the match function in javascript for regex

const str = 'For more information, see Chapter 3.4.5.1';
const re = /see (chapter d+(.d)*)/i;
const found = str.match(re);

console.log(found);

// logs [ 'see Chapter 3.4.5.1',
//        'Chapter 3.4.5.1',
//        '.1',
//        index: 22,
//        input: 'For more information, see Chapter 3.4.5.1' ]

// 'see Chapter 3.4.5.1' is the whole match.
// 'Chapter 3.4.5.1' was captured by '(chapter d+(.d)*)'.
// '.1' was the last value captured by '(.d)'.
// The 'index' property (22) is the zero-based index of the whole match.
// The 'input' property is the original string that was parsed.

js regexp match

// 1. Match indices for numbered group
const matchObj = /(a+)(b+)/d.exec('aaaabb');

console.log(matchObj);
/*
Output -
['aaaabb', 'aaaa', 'bb', index: 0, input: 'aaaabb', groups: undefined, indices: Array(3)]
*/
// then
matchObj.indices[1];
/*
Output - 
[0, 4]
*/
// -------------------------

// 2. Match indices for named groups
const matchObj = /(?<as>a+)(?<bs>b+)/d.exec('aaaabb');

console.log(matchObj);
/*
Output - 
['aaaabb', 'aaaa', 'bb', index: 0, input: 'aaaabb', groups: {as: 'aaaa', bs: 'bb'}, indices: Array(3)]
*/
// then
matchObj.indices.groups;
/*
Output -
{ as: [0,4], bs: [4,6] }
*/

js regexp match

// ES2022
const matchObj = /(a+)(b+)/d.exec('aaaabb');

console.log(matchObj);
/*
Output -
['aaaabb', 'aaaa', 'bb', index: 0, input: 'aaaabb', groups: undefined, indices: Array(3)]
*/