Question

Possible Duplicate:
Javascript: Do I need to put this.var for every variable in an object?

I ran into a problem with the following code:

var BuildMiniMap = function(camera, mapSize, width){

    this.camera = camera;
    this.canvas = document.getElementById('gameCanvas');
    this.mapSize = mapSize;
    this.width = width;
    this.height = Math.floor(mapSize[1]/(mapSize[0]/width));

    alert(canvas);
}

var miniMap = new BuildMiniMap(camera, [800, 600], 200);

Running it in a webpage will lead to an error in console:

Uncaught ReferenceError: canvas is not defined

And I have to use this.canvas instead. This only happens with canvas property, but not any other property. Does anyone know the reason and can provide an explanation? Thanks!

Answer 1

The other three properties, camera,mapSize and width are all defined as function arguments so are available within the function scope. canvas is not a function argument and is not defined inside the function so it doesn’t exist within the scope.