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 inputExample 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 matchExample 4: using regex in javascript
//Adding '/' around regex
var regex = /\s/g;
//or using RegExp
var regex = new RegExp("\s", "g");