Using the push method or .length when adding to array?

Question

What are the downsides to doing:

var myArray = [];
myArray[myArray.length] = val1;
myArray[myArray.length] = val2;

instead of:

Answer 1

As I tested, the first way is faster, I'm not sure why, keep researching. Also the ECMA doesn't mentioned which one is better, I think it is depending on how the browser vendor implements this.

var b = new Array();
var bd1 = new Date().getTime();
for(var i =0;i<1000000; i++){
    b[b.length] = i;
};

alert(new Date().getTime()- bd1);

var a = new Array();
var ad1 = new Date().getTime();
for(var i =0;i<1000000; i++){
    a.push(i);
};

alert(new Date().getTime()- ad1);