regular_expressions cheat sheet

Defining a pattern

var regex = /hello/;

methods

exec: return the result in an array if there is a match or null if not

var $pattern = /hello/;
$pattern.exec('hello');
// returns [ 'hello', index: 0, input: 'hello there', groups: undefined ]

$pattern.exec('something else');
// returns null

test: return true or false based on matching pattern

var $pattern = /hello/;
$pattern.test('hello');
// returns true

$pattern.test('something else');
// returns false

match: return the same result as exec if there is a match or null if not

var $str = 'hello';
$str.match(/hello/);
// returns [ 'hello', index: 0, input: 'hello there', groups: undefined ]

$str.match('something else');
// returns null

search: returns index of first match if not returns -1

var $str = 'hello there';
$str.search(/hello/);
// returns 0

$str.search(/there/);
// returns 6

$str.search(/something/);
// returns -1

replace: return new string with some or all matches of a pattern

var $str = 'hello there';

$str.replace(/hello/, 'Howdy');

Flags

i : case insensitive

var $pattern = /hello/i;

$pattern.test('Hello');
// returns true

$pattern.test('hero');
// returns false

g : global, look for all instances

var $pattern = /hello/g;

$pattern.exec('hello there hello');
// returns [ 'hello', index: 0, input: 'hello there hello', groups: undefined ]

$pattern.exec('hello');
// returns null : https://stackoverflow.com/questions/11270302/javascript-how-to-get-multiple-matches-in-regex-exec-results

$pattern.exec('something');
// returns null

Metacharacters

^ : Must start with

var $pattern = /^d/;

$pattern.test('dog');
// returns true

$pattern.test('cat');
// returns false

$ : must end with

var $pattern = /o$/;

$pattern.test('hello');
// returns true

$pattern.test('dog');
// returns false

. : any one character

var $pattern = /h.llo/;

$pattern.test('hello');
// returns true

$pattern.test('hrllo');
// returns true

$pattern.test('heddo');
// returns false

* : any character 0 or more

var $pattern = /h*llo/;

$pattern.test('heeeeeeeeeeeeeeello');
// returns true

$pattern.test('herer7&&&SDFasdf7llo');
// returns true

$pattern.test('hello!!!');
// returns false

$pattern.test('hllo');
// returns true

? : optional character

var $pattern = /gre?a?y/;

$pattern.test('grey');
// returns true

$pattern.test('gray');
// returns true

$pattern.test('groy');
// returns false

$pattern.test('gry');
// return true

\ : escape character

var $pattern = /gray\?/;

$pattern.test('gray?');
// returns true

$pattern.test('gray');
// returns false

Character Sets

[] : Must be any of the available options

var $pattern = /gr[ae]y/;

$pattter.test('gray');
// returns true

$pattern.test('grey');
// returns true

$pattern.test('gry');
// returns false

$pattern.test('grwy');
// returns false

[^] : Match anything except the available options

var $pattern = /[^gf]ray/;

$pattern.test('gray');
// returns false

$pattern.test('fray');
// returns false

$pattern.test('xray');
// returns true

[{} - {}] : match anything

var $pattern = /[A-Z]ray/;

$pattern.test('Xray');
// returns true

$pattern.test('xray');
// returns false

$pattern = /[A-Za-z]/;

$pattern.test('xray');
// returns true

$pattern.test('Xray');
// returns true

$pattern = /[0-9]ray/;

$pattern.test('9ray');
// returns true

$pattern.test('xray');
// return false

$pattern = /[0-9][0-9]ray/;

$pattern.test('99ray');
// return true

Quantifiers

symbol{min, max} : match the number of symbols specified before the curly brackets

var $pattern = /hel{2}o/i;

$pattern.test('hello');
// return true

$pattern = /hel{2, 4}o/i;

$pattern.test('helllo');
// return true

$pattern.test('helo');
// return false

$pattern = /hel{2,}o/;

$pattern.test('hello');
// return true

$pattern.test('helllllllllllllllo');
// return true

$pattern.test('helo');
// return false

Grouping

() : Groups expressions together, commonly used with quantifiers

var $pattern = /([0-9]x){3}/;

$pattern.test('1x2x3x');
// return true

$pattern.test('3x3x3x3x');
// return true

$patter = /^([0-9]x){3}$/;

$pattern.test('3x3x3x3x');
// return false

Word Characters

\w : word character alphanumeric or _

var $pattern = /\w/;

$pattern.exec('hello world');
// return [ 'h', index: 0, input: 'hello world', groups: undefined ]

$pattern = /\w+/; // + : one or more

$pattern.exec('hello world');
// return [ 'hello', index: 0, input: 'hello world', groups: undefined ]

$pattern.exec('');
// return null

\W : match an NON word or alphanumeric character

var $pattern = /\W/;

$pattern.test('1');
// return false

$pattern.test('a');
// return false

$pattern.test('_');
// return false

$pattern.test(' ');
// return true

$pattern.test('$');
// return true

\d : match any digit

var $pattern = /\d/;

$pattern.exec('1234');
// return [ '1', index: 0, input: '1234', groups: undefined ]

$patter.exec('abc');
// return null

$pattern = /\d+/; // + : one or more

$pattern.exec('1234');
// return [ '1234', index: 0, input: '1234', groups: undefined ]

$pattern.exec('1234 5678');
// return [ '1234', index: 0, input: '1234 5678', groups: undefined ]

\D : match any NON digit

var $pattern = /\D/;

$pattern.test('abc');
// return true

$pattern.test('123');
// return false

\s : match whitespace characters

var $pattern = /\s/;

$pattern.test('');
// return false

$pattern.test(' '); // <- thats a space
// return true

$patter.test('  '); // <- thats a tab
// return true

/S : match any NON whitespace characters

var $pattern = /\S/;

$pattern.test(' ');
// return falase

$pattern.test('abc');
// return true

\b : word boundary, if anything follows the boundary it is NOT a match

var $pattern = /hell\b/i;

$pattern.exec('Hello, welcome to Hell');
// return [ 'Hell', index: 17, input: 'Hello welcome to Hell', groups: undefined ]

$pattern = /hell/i;

$pattern.exec('Hello, welcome to Hell');
// return [ 'Hell', index: 0, input: 'Hello welcome to Hell', groups: undefined ]

$pattern = /\bhell/i;

$patter.exec('somethinghell');
// return null

$pattern.exec('hellsomething');
// return [ 'hell', index: 0, input: 'hellsomething', groups: undefined ]

Assertions

?= : Must follow after preceeding character

var $pattern = /x(?=y)/;

$pattern.test('x');
// return false

$pattern.test('xy');
// return true

$pattern.test('abcxyabc');
// return true

$pattern = /x(?!y)/; // ! : not equal

$pattern.test('xy');
// return false

$pattern.test('xabcy');
// return ture