Nice cheat sheet, did notice some type errors on the first for Loop: here's the corrected code: for (var i = 0; i < 10; i++) { console.log(i + ": " + i * 3 + "<br />"); } let a = [1, 2, 3]; var sum = 0; for (var i=0; i <a.length; i++) { sum += a[i]; } // pasing an array console.log(sum);