How to merge sorted arrays

sorted.js

function mergeSorted(a, b) {
	var array = new Array(a.length + b.length);
	var ii = a.length + b.length - 1;
	var jj = a.length - 1, kk = b.length - 1;
	while (jj >= 0 || kk >= 0) {
		array[ii--] = (jj < 0 || a[jj] < b[kk]) ? b[kk--] : a[jj--];
	}
	return array;
}

var a = [1, 3, 7, 9, 11];
var b = [2, 3, 4, 5, 12, 13];
console.log(mergeSorted(a, b));
// [ 1, 2, 3, 3, 4, 5, 7, 9, 11, 12, 13 ]