Invalid array length when trying to create an array from calculation

var map = {
    mapSize: 100, // the size of a side
    data: new Array(this.mapSize * this.mapSize),

    getIndex: function(x, y) {
        return x * this.mapSize + y;
    },

    getCoords: function(index) {
        var x = Math.floor(index/this.mapSize);
        return {
            x: x,
            y: index - (x * this.mapSize)
        }
    }
};

This code gives me RangeError: Invalid array length.
However when there is no calculation, like this:

data: new Array(this.mapSize),

it works.

Could you explain me why is that happening?