Every element in an array being incremented simultaneously when only one should be.

Question

I am using the following code to increment the elements in a 2d array surrounding a given element.

 EmptyCell = {number: 0}; //This has several parts in the actual code.
 list = new Array();

function init(w,h){
    for (var x = 0; x <= w; x++){
        list[x] = new Array();
        for (var y = 0 ; y <= h; y++){
            list[x][y] = EmptyCell;
        }
    }
}

function map(func,x,y){
    var xoff = [1,1,1,0,0,-1,-1,-1];
    var yoff = [1,0,-1,1,-1,1,0,-1];
    for (var atIndex = 0; atIndex < 8; atIndex++){
        func(x+xoff[atIndex],y+yoff[atIndex]);
    }
}

And then I run it like this:

init(10,10);

map(function(x,y){
    if (list[x] != null && list[x][y] != null){
        list[x][y].number++;
    }
},0,0);

Each time list[x][y].number++ is run, every element in the entire array is incremented. Could somebody explain why this is happening?

Answer 1

EmptyCell is an object, so all the elements reference the same object. If you want to use separate objects for each element, create a new instance each time.