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Regular Expressions

RegExp is a powerful object that matches text to a pattern.

There are two ways to create said object:

  • 1) Literal notation - pattern and/or options enclosed by / /

  • 2) Constructor - take in a string or literal and option flags as parameters

The following 3 expressions create the same exact regular expression object:

info

The 'i' is one of many flags, specifically for making the search case-insensitive.

Let's breakdown the regular expression /ab+c/:

  • + after b means to match at least one 'b'

  • 'a' and 'c' are simply the beginning and end of the pattern

    • 'abc' matches, as well as 'abbbc'. 'ababc' does not

A great example is /be+/: 'bee', 'bent', 'bear' are all matches.

Character classes and Anchors​

A character class matches any one set of characters.

Here are some examples:

  • [ae] matches the "a" in "based", and "e" in "lane"

  • [^ae] matches anything not in the character class - "r", "g", "n" are matched in "green"

  • [A-P] matches any character in the range A through P

  • \w matches any word character - "V", "e", "2", "0", not "." in "Ve2.0"

Anchors cause a match to succeed or fail based on the current position in the string.

They don't cause advancement through the string or consume characters.

Here's a few examples:

  • $ match must occur at the end

  • \A match must occur at the start of the string

  • \b match must occur on a boundary between a word character and a non-word character

tip

RegExp can be an extremely powerful tool, but it may be complicated at first.

If you wish to learn more about

  • If you wish to learn more about character classes, anchors, and regular expressions in general, visit: RegExp - MDN.