{ Metacharacters and Grouping. }


By the end of this chapter, you should be able to:

  • Use common metacharacters to write more succinct regular expressions
  • Create word boundaries and groups for more efficient regular expressions
  • Write regular expressions for more complex types of validation and pattern matching


So far we have seen how to match certain kinds of characters a specific number of times. While this is a good start, we can improve our usage of regular expressions by understanding metacharacters, which are certain characters that can be prefixed with a \. Let's take a look:


This matches a digit character. Instead of using [0-9], we can use \d:

var simplePhoneRegex = /[0-9]{3}-[0-9]{3}-[0-9]{4} /
var betterPhoneRegex = /\d{3}-\d{3}-\d{4}/
var str = "My number is 201-867-5309"
str.match(betterPhoneRegex) // ["201-867-5309"]


This matches a non-digit character. We will see that the capitalized versions of metacharacters are equivalent to the not of the lower case metacharacter.

var noNumbers = /\D+/g
var str = "H3ll0"
str.match(noNumbers) // ["H", "ll"]

\n, \r and \t

These characters match newlines, carriage return, and tab characters, respectively:

"this is \n a string \n on many \n lines".match(/\n/g) // returns an array of three newlines


This character matches any whitespace character:

"please remove all the white space now".replace(/\s/g,'') // "pleaseremoveallthewhitespacenow"


This character matches any non-whitespace character:

"please remove everything but the white space now".replace(/\S/g,'') // "       "


This character matches any word character. Notice what is defined as a word character below. In particullar, numbers count as word characters!

"pl3ease r3mov3 ALL 12the 44word characters__. So what is left? Maybe [] or {} or () or [email protected]#$%^&*".replace(/\w/g,'') // "     .    ?  []  {}  ()  [email protected]#$%^&*"


This characters matches any non-word character which includes spaces, special characters ([email protected]#$%*() and whitespace characters):

"j ".replace(/\W/g,'wow') // "jwow"

Special characters

starting - ^

If we want to match starting from the beginning of a string, we can use the ^ character:

"this is great".match(/^t.*/) // ["this is great"]
"now this is not great".match(/^t.*/) // null

ending - $

If we want to match something that specifically ends with a character we use $:

"first.test.js".match(/.*\.test.js$/) // ["first.test.js"]
"first.js".match(/.*\.test.js$/) // null

excluding ^ (inside [])

If we want to exclude something in a character set we use ^ inside []:

"let's get rid of everything that is not a vowel".replace(/[^aeiou]/gi,'') // "eeioeeiaioaoe"

or - |

If we want to handle multiple conditions we can use the or operator with a |. If you find yourself using multiple | operators, there is usually a better regular expression for the job.

"banana bread".match('bread|pancakes$') // ["bread"]
"banana pancakes".match('bread|pancakes$') // ["pancakes"]

word boundaries - \b

The metacharacter \b matches the boundary between a word and a non-word character. It is used commonly when capturing entire words between non character words. The pattern for that is /\w+\b/.

"my email is. . . . . . [email protected]".match(/\b/g).length // 12 - why does this return 12? Count each start and end of a word (between non character word)

// my
// email
// is
// elie
// rithmschool
// com

// => 6 * 2 = 12

// Now let's use word boundaries a bit better!

"my email is. . . . . . . [email protected]".match(/\w+\b/g) // ["my", "email", "is", "elie", "rithmschool", "com"]

"http://www.google.com".match(/\w+\b/g) // ["http", "www", "google", "com"]

Groupings - ()

A more advanced concept in regular expressions is the idea of creating groups which you can later access. To create a group, we use the () characters. We can then refer to these groups as $1, $2, and so on.

var tweet = "This is the best tweet #amazing #perfect #sogood";
var regex = /#([\S]+)/ig;

var matches = tweet.match(regex);

matches.map(v => v.replace(regex, 'hashtag: $1')) // ["hashtag: amazing", "hashtag: perfect", "hashtag: sogood"]

If we want to iterate over multiple groups, we can loop and continue to use the exec function. You can read more about that here

External Resources



When you're ready, move on to Regular Expressions Exercises


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