Question

When using Javascript as follows:

function Test(Example) {
}

Test.prototype.etc etc etc


function Example() {
}


Example.prototype.etc etc etc


example = new Example();
test = new Test(example);

Is this efficient or am I hogging memory somehow?

I ask this as I have the following setup within my javascript game at present and each requires some of the other (in brackets):

Camera (canvas)
Input (canvas, camera, tilemap)
Sprite (camera, canvas)

Am I going about this the wrong way? Should I be passing this method some other way? It’s struck me as a concern as I now have quite a few new instances of sprite and wondered if it is going to become a problem.

Cheers

Answer 1

JavaScript objects (and functions) are not copied when they are passed as parameters. Take a look at the following code (or test it on JSFiddle):

function Foo() {};
Foo.prototype.property = 5;
function incrementProperty(parameter) { parameter.property++; };

var foo = new Foo();

alert(foo.property); // 5
incrementProperty(foo);
alert(foo.property); // 6
alert(new Foo().property); // 5, because it's a new object

The foo object is not copied when it is passed to the bar function. This is demonstrated by the fact that foo‘s property retains is value back outside of the method. Put simply, foo and parameter point to the same object.

Keep in mind that they themselves aren’t the same object, though. If you reassign parameter to point to new value within the bar function (parameter = "dummy";), foo will be not be affected. Does that distinction make sense?

Note: JavaScript strings and numbers are copied when they are passed as parameters, though.