Metacharacters, Flags and Regular Expressions in JavaScript

Not all characters can be used "as is" in a match. Some characters, called metacharacters, are reserved for use in regexp notation. The metacharacters are

{} [] () ^ $ . | * + ? /

These characters are used to give meaning to the regexp object.

A metacharacter can be matched by putting a backslash before it. Here are some examples:

/2+2/.test("2+2=4") // doesn't match, '+' is a metacharacter

/2+2/.test("2+2=4") // matches because '+' is treated like an ordinary '+'

/C:WIN/.test("C:WIN32") // matches (MS DOS path)

//usr/bin/perl/.test("/usr/bin/perl") // matches

Combining Matching Features

You can combine matching features. We have seen some of these, such as in /[cbr]at/. Here are more examples:

/[a-z]+s+d*/.test(available string)

This matches a lowercase word, at least some space, and any number of digits.

/(w+)s+1/.test(availablestring)

This matches doubled words of arbitrary length.

/d{2,4}/.test(year)

This is to verify that the year is at least two but not more than four digits.