Interesting usage of bound functions as "partial" constructor

function Area(width, height) {
    this.width = width;
    this.height = height;
    this.area = function () {
        return this.width * this.height;
    };
}

var PartialConstructor = Area.bind(null, 5);
var o1 = new PartialConstructor(5);
var o2 = new PartialConstructor(10);

o1.area(); // 25
o2.area(); // 50

More details on MDN (see Bound functions used as constructors).