My attempt at solving https://gist.github.com/3134886

solution.js

function Point(a, b) {
    if (arguments.length === 1) {
        this.x = Math.round(a / 1000);
        this.y = a - this.x * 1000;
    } else {
        this.x = a;
        this.y = b;
    }
}

Point.prototype.valueOf = function () {
    return this.x * 1000 + this.y;
}

Point.prototype.toString = function () {
    return "{" + this.x + "," + this.y + "}";
}


new Point(new Point(10, 20) + new Point(30, 50)).toString() // === "{40,70}"

Nice!