Struct in JavaScript

Hello,

Is there a way to make a structure in JavaScript? I mean not class but structure as Vector3 for example. For creating big fast arrays. Something like this:

struct SomeStruct{
var i : int;
var f : float;
}

var arr = new SomeStruct[1000];
arr[500].a = 3;

In a case of class I need to initialize every member of the array...