2-dimensional "wrapping" array

I'm writing a simple JavaScript game, which uses a 2-dimensional array as the main data structure. I wrote this function-class-thing that allows me to give any two integers, positive or negative. This class should "wrap" those integers back onto the game grid.

For example:

var g = new Grid(10, 10)
g.set(15, -2, "hello")
g.get(5, 8); //should be "hello"

Anyway, I'm striving to improve my JavaScript, so I'm wondering if there are any improvements (performance, "javascriptness", etc.) that I might be able to make.

var Grid = (function(w, h){
    this._width = w;
    this._height = h;
    this._grid = new Array((this._width * this._height) | 0);
    this.get = function(x, y){
            var coords = _normalize(x, y);
            return this._grid[(coords.y * coords.x) + coords.x];
    }
    this.set = function(x, y, item){
            var coords = _normalize(x, y);
            this._grid[(coords.y * coords.x) + coords.x] = item;
    }
    this._normalize = function(x, y){
            if(x = this._width) x = x % this._width ;
            if(y = this._height) y = y % this._height;
            return {'x': x, 'y': y};
    }
});

I can't say, that my variant of normalize function is easier to understand, but at least it is linear and it works correct (as i think) with x, that is less than -width

this._normalize = function(x, y) {
    x = x % this._width;
    y = y % this._height;

    x = (this._width + x) % this._width;
    y = (this._height + y) % this._height;

    return {'x': x, 'y': y};
}

Also, you missed this statement in get and set functions (looks like a typo):

this.get = function(x, y){
    var coords = this._normalize(x, y);
    return this._grid[(coords.y * coords.x) + coords.x];
}
this.set = function(x, y, item){
    var coords = this._normalize(x, y);
    this._grid[(coords.y * coords.x) + coords.x] = item;
}

It is better to move get, set and normalize functions to Grid prototype.
Putting these functions in prototype will increase execution speed and require less memory for creating an instance of Grid because these functions will not
be created every time Grid instance is created.
Like this:

var Grid = function(w, h){
    this._width = w;
    this._height = h;
    this._grid = new Array((this._width * this._height) | 0);
};
Grid.prototype.get = function(x, y) {
    // get code
};
Grid.prototype.set = function(x, y, item){
    // set code
};
Grid.prototype._normalize = function(x, y){
    // normalize code
};

StackExchange Code Review Q#32512, answer score: 3