How to calculate length?

Question

<script>
var num1= [1,2];
var num2=[3,4];
var set=num1+ num2 ;
document.write(set.length);
</script>

Answer 1

num1.push(num2)

Answer 2

You mean the length or the result

Answer 3

Both

Answer 4

If you want Merge two array you must define array in first , for your case you must define
var set =new Array(4);
Now you allocated
Then you must using for loop to put num1 and num2 to empty Array set