Question

If subclassing a “class” in JavaScript is done like so:

var ParentClass = function() {
    // something
};


var ChildClass = function() {
    // something
};

ChildClass.prototype = new ParentClass();

… what should I do when the parent class has required parameters?

var ParentClass = function(requiredParameter) {
    if (typeof requiredParameter === 'undefined') {
        throw new TypeError("'requiredParameter' is required!");
    }
};


var ChildClass = function() {
    // something
};

ChildClass.prototype = new ParentClass();
// ^ Throws TypeError

Thanks.

Answer 1

Subclass it like this instead:

function clone (obj) {
  if (!obj) return;
  clone.prototype = obj;
  return new clone();
}

var ParentClass = function() {
    // something
};


var ChildClass = function() {
    // something
};

ChildClass.prototype = clone(ParentClass.prototype);
ChildClass.prototype.constructor = ChildClass; // if you want

Now you don’t have to worry about it, because you don’t have to call the parent constructor to subclass it 🙂