regex pattern visualizer : regex101: build, test, and debug regex https://regex101.com/
regex
regex character
| character | meaning |
|---|---|
| \d | digital characters |
| \D | not digital characters |
| \w | Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to [A-Za-z0-9_]. |
| \W | Matches any character that is not a word character from the basic Latin alphabet. Equivalent to [^A-Za-z0-9_]. |
| \s | Matches a single white space character, including space, tab, form feed, line feed, and other Unicode spaces. Equivalent to [\f\n\r\t\v\u0020\u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff]. For example, /\s\w*/ matches " bar" in "foo bar". |
| \b | word boundary. "\baa\b.*" matches "aa bb", dose not match "aabb". |
look ahead and look behind
| Lookaround | Name | What it Does |
|---|---|---|
| (?=foo) | Lookahead | Asserts that what immediately follows the current position in the string is foo |
| (?<=foo) | Lookbehind | Asserts that what immediately precedes the current position in the string is foo |
| (?!foo) | Negative Lookahead | Asserts that what immediately follows the current position in the string is not foo |
| (?<!foo) | Negative Lookbehind | Asserts that what immediately precedes the current position in the string is not foo |
lazy vs greedy
| type | pattern | description |
|---|---|---|
| greedy | .* | matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy) |
| lazy | .*? | matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy) |
ref
Lookahead and Lookbehind Tutorial—Tips &Tricks
https://www.rexegg.com/regex-lookarounds.html
Regex Tutorial - Lookahead and Lookbehind Zero-Length Assertions
https://www.regular-expressions.info/lookaround.html
Regular expressions - JavaScript | MDN
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions
Character classes - JavaScript | MDN
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Character_Classes