how to create regex in javascript code example

Example 1: javascript regex

//Declare Reg using slash
let reg = /abc/
//Declare using class, useful for buil a RegExp from a variable
reg = new RegExp('abc')

//Option you must know: i -> Not case sensitive, g -> match all the string
let str = 'Abc abc abc'
str.match(/abc/) //Array(1) ["abc"] match only the first and return
str.match(/abc/g) //Array(2) ["abc","abc"] match all
str.match(/abc/i) //Array(1) ["Abc"] not case sensitive
str.match(/abc/ig) //Array(3) ["Abc","abc","abc"]
//the equivalent with new RegExp is
str.match('abc', 'ig') //Array(3) ["Abc","abc","abc"]

Example 2: javascript regex reference

// Javascript Regex Reference
//  /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 3: regular expression flags

Besides the regular expressions, flags can also be used to help developers with pattern matching.
/* matching a specific string */
regex = /sing/; // looks for the string between the forward slashes 9case-sensitive)… matches “sing”, “sing123”
regex = /sing/i; // looks for the string between the forward slashes (case-insensitive)... matches "sing", "SinNG", "123SinNG"
regex = /hello/g; // looks for multiple occurrences of string between the forward slashes...
/* groups */
regex = /it is (sizzling )?hot outside/; // matches "it is sizzling hot outside" and "it is hot outside"
regex = /it is (?:sizzling )?hot outside/; // same as above except it is a non-capturing group
regex = /do (dogs) like pizza 1/; // matches "do dogs like pizza dogs"
regex = /do (dogs) like (pizza)? do 2 1 like you?/; // matches "do dogs like pizza? do pizza dogs like you?"
/* look-ahead and look-behind */
regex = /d(?=r)/; // matches 'd' only if it is followed by 'r', but 'r' will not be part of the overall regex match
regex = / (?<=r)d /; // matches 'd' only if it is proceeded by an 'r', but 'r' will not be part of the overall regex match

Example 4: using regex in javascript

//Adding '/' around regex
var regex = /\s/g;
//or using RegExp
var regex = new RegExp("\s", "g");

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