History of Regular Expression

• concept developed in 1950 by mathematician Stephen Keene
• Became regularly used by Unix text processing utilities.
• Many different variations became standardized by the POSIX standard
• A version of regular expressions was used in Perl in the 1980s.
• In 1997 Philip Hazel developed PCRE for use in many modern tools

create a RegEx in JS

• let regex1 = new RegExp(’hello’)
• let regex2 = /world/

About Methods

RegExp Methods

• test: returns true if pattern is found in the passsed string; false if not
• exec: returns an array of matches
• toString: returns a string of the regular expressions syntax

String Methods

• match: returns an array of matches just like exec on RegExp.
• search: returns an index of the matched string
• replace: replaces matches with string
• split: splits a string into an array. The division is based on the regular expression pattern

Regular Expression Flags

• /pattern/flags or new RegExp(”pattern”, “flags”)
• g match more than one occurance
• i insensitive match
• m multi-line match

That Metacharacters

• wildcard . It represents any single character
• escaped character \ It mathces a “.” character
• hyphen - like 0-9 or a-z
• square brace [] range
• + Matches one or more occurrences
• ? Matches zero or one occurrences
• *. Matches zero or more occurrences
• {min,} {min, max} {min}
• \b Word boundary-Pattern bounded by a non-word character
• \B Nonword boundary-Pattern bounded by a word character

Character Set Shorthand

• \d [0-9] \D [^0-9]
• \w [a-zA-Z0-9_] \W [^a-zA-Z0-9_]
• \s [\t\r\n] \S [^\t\r\n]

Groupback reference

• non capture group 使用 ?: 比如 (?:\w+)

unicode character