Regular Expression Flag | JavaScript Tutorial

RegExp.prototype.test()

It accepts a string that we test against a regular expression and returns either trueor falseRegExp.prototype.exec()

let regex = /hello/; 
let str = 'hello world';
let result = regex.test(str);
console.log(result); 
// returns 'true' as hello is present in our string

RegExp.prototype.exec()

receive an array of all the matched groups. It accepts a string that we test against our regular expression.

let regex = /hello/;
let str = 'hello world';
let result = regex.exec(str);
console.log(result);
// returns [ 'hello', index: 0, input: 'hello world', groups: undefined ]

Flags:

In any regular expression, we can use the following flags:

• g: matches the pattern multiple times
• i: makes the regex case insensitive
• m: and enables multi-line mode. Where ^ and $ match the start and end of the entire string. Without this, multi-line strings match the beginning and end of each line.
• u: enables support for Unicode
• s: short for single line, it causes the . to also match new line characters

Flags may also be combined in a single regular expression & the flag order doesn’t matter. They are added at the end of the string in regex literals:

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/hello/ig.test('HEllo')
// returns true

If using RegExp object constructors, they’re added as the second parameter:

new RegExp('hello', 'ig').test('HEllo') 
// returns true

Meta-characters

Meta-characters are characters with a special meaning. Let’s take a look at some of these here:

• \d : matches any digit, being[0-9]
• \D: matches any character that is not a digit, effectively[^0-9]
• \w: matches any alphanumeric character (plus underscore), equivalent to [A-Za-z_0-9]
• \W: matches any non-alphanumeric character, so anything except [^A-Za-z_0-9]
• \s: matches any whitespace character: spaces, tabs, newlines and Unicode spaces
• \S: matches any character that is not a whitespace
• \0: matches null
• \n: matches a newline character
• \t: matches a tab character
• \uXXXX: matches a unicode character with code XXXX (requires the u flag)
• .: matches any character that is not a newline char (e.g. \n) (unless you use the s flag, explained later on)
• [^]: matches any character, including newline characters. It’s very useful on multi-line strings

reference: https://www.easeout.co/blog/2022-01-03-understanding-regex/