2023-08-11.js

// https://www.codewars.com/kata/559536379512a64472000053/train/javascript
function playPass( s, n ) {
	const a = 'abcdefghijklmnopqrstuvwxyz';
	return s.split( '' )
		.map( ( c, i ) => {
			if ( /[A-z]/.test( c ) ) {
				const idx = ( a.indexOf( c.toLowerCase() ) + n ) % 26;	// #1: shift n, % => "circular shift"
				return i%2 === 0 ? a[idx].toUpperCase() : a[idx];		// #4: even/odd uppercase/lowercase
			} else if ( /[0-9]/.test( c ) ) {
				return 9 - c; 											// #2: digit by its complement to 9
			} else {
				return c; 												// #3: keep non alpha/digit
			}
		} )
		.reverse() 														// #5: reverse
		.join( '' );
}
console.log( playPass( 'BORN in 2015!', 1 ) ); // :>> "!4897 Oj oSpC"
console.log( playPass( 'I LOVE YOU!!!', 1 ) ); // :>> "!!!vPz fWpM J"
console.log( playPass( 'MY GRANMA CAME FROM NY ON THE 23RD OF APRIL 2015', 2 ) );