apply() in JavaScript

function ClassA(sColor) {
    this.color = sColor;
    this.sayColor = function () {
        alert(this.color);
    };
}

function ClassB(sColor, sName) {
    ClassA.apply(this, arguments);
    this.name = sName;
    this.sayName = function () {
        alert(this.name);
    };
}

var objA = new ClassA("red");
var objB = new ClassB("blue", "Nicholas");
objA.sayColor();
objB.sayColor();
objB.sayName();