Regular Expressions (RegEx)

Allows us to check a series of characters for 'matches'. Use the regex101 online tool to create test patterns.

Simple Patterns

• /pattern/ looks for the first instance
• /pattern/g, the g flag makes the search global
• /pattern/gi, the i flag makes the search match case insenstive

Character Sets

• [], the character set
• /[ph]attern/, matches either a p or a h in the first position and occupies one space in the whole regular expression
• [^p]000, the ^ carrot excludes the p from the match

Ranges

• /[a-z]attern/g, includes all the letters of the alphabet
• /[a-z]attern/gi add the i case insensitive flag OR use the following; /[a-zA-Z]attern/
• /[0-9]attern/g

Repeating Characters

• /[0-9]+/, the + sign allows a match for the numbers in the range 0 to 9 for any length
• /[0-9]{11}/, create a match for a number 11 times
• /[a-z]{11}/ matches an 11 letter word
• /[a-z]{5, 8}/ matches a word between 5 and 8 characters long
• /[a-z]{5,}/ matches anything at least 5 characters long

Metacharacters

Check out this link for more metacharacters but here are the more common ones:

• \d match any digit character (same as [0-9])
• \w match any word character (a-z, A-Z, 0-9 and _'s)
• \s match a whitespace character (spaces, tabs, etc.)
• \t match a tab character only
• d -- matches the literal character, 'd'
• \d-- matches any digit character For example; /\d\s\w/ will produce a match for the 1 w and the 5 p pattern

Special Characters

• + the one-or-more quantifier
• \ the escape character
• [] the character set
• [^] the negate symbol in a character set
• ? the zero-or-one quantifier (makes the preceding character optional) e.g. /he?llo?/g, the e and o is optional
• . any character whatsoever (except the newline character) e.g. /car./g will match card or cart
• * the 0-or-more quantifier (a bit like +) e.g. /a[a-z]*/g
• The backslash, \ is the escape character e.g. /abc\./g

Starting & Ending Patterns

• /[a-z]{5}/gi will still match more than 5 characters, give it a go
• /^[a-z]{5}$/gi, the carrot symbol ^ in the beginning and the dollar sign $ at the end will produce a match for 5 characters only

Alternate Characters

• A single pipe | in regex means OR
• /p|t/i will match only either p or t
• /(p|t)yre/i, use parentheses to evaluate a part of the expression separately before moving on
• /(crazy|pet|toy) rabbit/gi or /(crazy|pet|toy)? rabbit/gi, remember everything before the ? is optional

How to create Regular Expressions?

// store in a variable
var reg = /[a-z]/gi;
//OR
var reg2 = new RegExp(/[a-z]/, 'i');