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);