Google maps javascript issue

Question

I am seeing something I don't understand when using the Google map API. I have the following code to pull the viewport...

var bounds = map.getBounds();
var viewport = {
    top: bounds.getNorthEast().lat(),
    right: bounds.getNorthEast().lng(),
    bottom: bounds.getSouthWest().lat(),
    left: bounds.getSouthWest().lng()
};

Turns out that viewport.top returns...

57.220445088498764 {
    toJSON : function(key) { return this.valueOf(); } }

Can someone explain to me what this is? I don't completely understand js prototypes, but based on my limited understanding a js prototype is a function attached to an instance of an object. Since a number is an object, has Google placed a prototype function called 'toJSON' on all objects it returns?

How can I get rid of that so I end up with simply the number 57.220445088498764?

I am attempting to use the json2.js JSON.stringify, and it isn't giving proper JSON back because of this weird function.

What's the problem with the way things are working now? Having an extra function on the Number prototype shouldn't hurt anything (or at least not anything you'd run into ordinarily). Getting rid of that function might be a really bad idea, as other parts of the Google API may rely on it. — Pointy
– Pointy, Commented Aug 19, 2011 at 22:18

plexer · Accepted Answer · 2011-08-21 04:26:51Z

1

In Javascript everything is an Object** - even Numbers. This means that we can add methods to anything - even numbers. Try this in Firebug or the Chrome inspector:

Number.prototype.hello = function() { alert("Hello, world!"); }

var x = 2;
x.hello();

Even though x is a number, it can still have methods. By adding a method to the prototype for Number, we ensure that all numbers have that method. Of course, normal numbery things will still work too:

var y = x + 2;
window.console.log(y); // Will output 4.

This seems to be used by the Maps API to add a toJSON method to numbers for convinience. It isn't a great design strategy in my opinion, but it's also harmless. Your number will continue to act just like a number should, so you can safely ignore the toJSON method.

** Except the things that aren't, like number or string literals.

answered Aug 21, 2011 at 4:26

plexer

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