() in regex javascript code example

Example 1: javascript regex

// \d	Any digit character
// \w	An alphanumeric character (“word character”)
// \s	Any whitespace character (space, tab, newline, and similar)
// \D	A character that is not a digit
// \W	A nonalphanumeric character
// \S	A nonwhitespace character
// .	Any character except for newline
// /abc/	A sequence of characters
// /[abc]/	Any character from a set of characters
// /[^abc]/	Any character not in a set of characters
// /[0-9]/	Any character in a range of characters
// /x+/	One or more occurrences of the pattern x
// /x+?/	One or more occurrences, nongreedy
// /x*/	Zero or more occurrences
// /x?/	Zero or one occurrence
// /x{2,4}/	Two to four occurrences
// /(abc)/	A group
// /a|b|c/	Any one of several patterns
// /\d/	Any digit character
// /\w/	An alphanumeric character (“word character”)
// /\s/	Any whitespace character
// /./	Any character except newlines
// /\b/	A word boundary
// /^/	Start of input
// /$/	End of input

Example 2: what is regular expression in javascript

let re = /ol/, 
Characters \, ., \cX, \d, \D, \f, \n, \r, \s, \S, \t, \v, \w, \W, \0, \xhh, \uhhhh, \uhhhhh, [\b]	
Assertions 	^, $, x(?=y), x(?!y), (?<=y)x, (?<!y)x, \b, \B
Groups 		(x), (?:x), (?<Name>x), x|y, [xyz], [^xyz], \Number	
Quantifiers *, +, ?, x{n}, x{n,}, x{n,m}
Unicode \p{UnicodeProperty}, \P{UnicodeProperty}	 property escapes
let defaults = new RegExp('compiled'); 
defaults = { dotAll: false, flags: "", global: false, ignoreCase: false, falselastIndex: 0, multiline: false, source: "abc", sticky: false, unicode: false}