What's the difference between Array(1) and new Array(1) in JavaScript?

Question

I just started thinking about this, but couldn\'t get any differences to expose themselves whilst mucking around in jsFiddle.

var a = new Array(1),
    b = A         


        

Answer 1

The difference lies in the implementation of the Array function. Whether a call to Array without a new operator will return an instance of Array or not is implementation dependent. For example Mozilla's SpiderMonkey engine does this:

static JSBool
Array(JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval *rval)
{
     jsuint length;
     jsval *vector;

     /* If called without new, replace obj with a new Array object. */

That is an actual comment from the actual source. Next lines of code are not reproduced here. I would suppose other engines do the same. Otherwise the behavior is undefined. A good read on this topic is John Resig's post here.