Newbie Javascript : appending to array

Question

OK.

How do I append to an array in Javascript?

Update : actually

a.push(b)

does work. Realize that my previous problem was b not having a value.

Ok, I answered myself, but might as well leave this here on SO to help other newbies.

Answer 1

var arr = new Array(3);
arr[0] = "Hi";
arr[1] = "Hello";
arr[2] = "Bonjour";
arr.push("Hola");
for (var i = 0; i < arr.length; i++) {
    alert(arr[i]);
};

Answer 2

Is b a variable? If not, it probably needs quotes.

Also, lots of good info on JavaScript push() method here.

Answer 3

If you're only appending a single variable, than your method works just fine. If you need to append another array, use concat(...) method of the array class:

var ar1 = [1, 2, 3];
var ar2 = [4, 5, 6];

var ar3 = ar1.concat(ar2);

alert(ar3);

Will spit out "1,2,3,4,5,6"

Lots of great info here

Answer 4

Some quick benchmarking (each test = 500k appended elements and the results are averages of multiple runs) showed the following:

Firefox 3.6 (Mac):

• Small arrays: arr[arr.length] = b is faster (300ms vs. 800ms)
• Large arrays: arr.push(b) is faster (500ms vs. 900ms)

Safari 5.0 (Mac):

• Small arrays: arr[arr.length] = b is faster (90ms vs. 115ms)
• Large arrays: arr[arr.length] = b is faster (160ms vs. 185ms)

Google Chrome 6.0 (Mac):

• Small arrays: No significant difference (and Chrome is FAST! Only ~38ms !!)
• Large arrays: No significant difference (160ms)

I like the arr.push() syntax better, but I think for my use I'd be better off with the arr[arr.length] version, at least in raw speed. I'd love to see the results of an IE run though.

---

My benchmarking loops:

function arrpush_small() {
    var arr1 = [];
    for (a=0;a<100;a++)
    {
        arr1 = [];
        for (i=0;i<5000;i++)
        {
            arr1.push('elem'+i);
        }
    }
}

function arrlen_small() {
    var arr2 = [];
    for (b=0;b<100;b++)
    {
        arr2 = [];
        for (j=0;j<5000;j++)
        {
            arr2[arr2.length] = 'elem'+j;
        }
    }
}


function arrpush_large() {
    var arr1 = [];
    for (i=0;i<500000;i++)
    {
        arr1.push('elem'+i);
    }
}

function arrlen_large() {
    var arr2 = [];
    for (j=0;j<500000;j++)
    {
        arr2[arr2.length] = 'elem'+j;
    }
}