https://lingfieldparishchurch.org/js/jquery-plugins/jquery.validate/additional/creditcard.js?v=5

1// https://jqueryvalidation.org/creditcard-method/
2// based on https://en.wikipedia.org/wiki/Luhn_algorithm
3$.validator.addMethod( "creditcard", function( value, element ) {
4	if ( this.optional( element ) ) {
5		return "dependency-mismatch";
6	}
7
8	// Accept only spaces, digits and dashes
9	if ( /[^0-9 \-]+/.test( value ) ) {
10		return false;
11	}
12
13	var nCheck = 0,
14		nDigit = 0,
15		bEven = false,
16		n, cDigit;
17
18	value = value.replace( /\D/g, "" );
19
20	// Basing min and max length on
21	// https://dev.ean.com/general-info/valid-card-types/
22	if ( value.length < 13 || value.length > 19 ) {
23		return false;
24	}
25
26	for ( n = value.length - 1; n >= 0; n-- ) {
27		cDigit = value.charAt( n );
28		nDigit = parseInt( cDigit, 10 );
29		if ( bEven ) {
30			if ( ( nDigit *= 2 ) > 9 ) {
31				nDigit -= 9;
32			}
33		}
34
35		nCheck += nDigit;
36		bEven = !bEven;
37	}
38
39	return ( nCheck % 10 ) === 0;
40}, "Please enter a valid credit card number." );