global. Find all matches. Don't stop after first found.
i
ignore case
m
multiline; make the regex syntax ^ and $ match any newline beginning/end. (not just the beginning/end of whole string)
y
sticky; matches only from the index indicated by the lastIndex property of this regular expression in the target string (and does not attempt to match from any later indexes). This allows the match-only-at-start capabilities of the character "^" to effectively be used at any location in a string by changing the value of the lastIndex property.
// example of regex matching unicode by hex codepoint
var xx = "alpha α";
console.log(xx.search(/\u03b1/)); // 6
console.log(xx.search(/α/)); // 6. literal Unicode is ok too.
Character Sets, Character Classes
Regex Character Classes
syntax
meaning
[…]
any character between the brackets.
[^…]
any char that's not one of the character in the brackets.
.
any char, except newline characters: {\n, \r, \u2028, \u2029}.
Regex Character Classes
syntax
meaning
\w
any letter (upper or lower) or digit.
\W
any character that is not \w.
\d
any ASCII digit 0 to 9.
\D
Any character that's not \d.
\s
any Unicode whitespace character.
\S
any character that is not \s.
Boundaries
Regex Character Classes
syntax
meaning
^
beginning of string. If flag /…/g is set, also match beginning of line.
$
end of string. If flag /…/g is set, also match end of line.
\b
word boundary. For literal backspace, use [\b]
\B
Not word boundary.
Repetition
Regex Repetition Syntax
Syntax
Meaning
*
Match previous pattern 0 or more times. Same as {0,}.
?
Match previous pattern 0 or 1 time. Same as {0,1}.
+
Match previous pattern 1 or more times. Same as {1,}.
{n}
Match previous pattern exactly n times.
{n,}
Match previous pattern n or more times.
{n,m}
Match previous pattern n times or up to m times (inclusive).
Note: these will match as far as possible. For non-greedy version, add a ? after them.
Alternate and Conditions
Regex Repetition Syntax
Syntax
Meaning
x|y
Alternate. Matches either x or y
x(?=y)
Matches only if x is followed by y
x(?!y)
Matches only if x is not followed by y
Capture Grouping, Back Reference
Regex Repetition Syntax
Syntax
Meaning
(…)
Capture. Captured group can be later referenced by /n where n is a digit. \1 is the first captured group.
(?:…)
Group, but don't captured.
/n
The nth captured group before. \1 is the first captured group.