how does this program work?

<script>
classa=function(array)
{
return new classa.prototype.init(array);
}

classa.prototype={
init:function(array)
{
return this.setArray(array);
},
setArray : function(elems) {
this.length = 0;
Array.prototype.push.apply(this, elems);
return this;
}

}
classa.prototype.init.prototype=classa.prototype;
alert(classa([1,2,3])[0]);
alert(typeof(classa([1,2,3]));
</script>

this program was changed from source code of "jquery",
I don't know why classa([1,2,3]) can use like a array,
I don't how how keywords "new" works here, what "this" point step by step,
who can analysis this program for me ,any answer will be greatly appreciated.

Do research in OO JavaScript. Plenty of material out there that will teach you how it works.

[1,2,3] is array notation. Any intro book to JavaScript will explain it.

Eric

Here's a good intro
http://w3schools.com/js/js_obj_intro.asp