Issue with JavaScript object constructor where arguments are other objects

Question

I'm writing some JavaScript with three classes, one for Roofs, one for Garages, and one for Houses. The house class takes two arguments to its constructor, a Roof and a Garage. When I run this code I get:

can not construct object [Break on this error] throw new Error('can not construct object');\n

in Firebug even though the objects are clearly of the right type. Any idea what I'm doing wrong? Here's the code:

function Roof(type, material) {
     this.getType = function() { return type; }
     this.getMaterial = function() { return material; }
}

function Garage(numberOfCars) {
     this.getNumberOfCars = function() { return numberOfCars; }
}

function House(roof, garage) {
     if (typeof roof !== 'Roof' || typeof garage !== 'Garage') {
          throw new Error('can not construct object');
     }

     this.getRoof = function() { return roof; }
     this.getGarage = function() { return garage; }
}

myRoof = new Roof("cross gabled", "wood");
myGarage = new Garage(3);
myHouse = new House(myRoof, myGarage);
alert(myHouse.getRoof().getType());

Answer 1

The typeof operator will return "object" for your objects, not their names. See the typeof Operator documentation.

function House(roof, garage) {
    alert(typeof roof);   // "object"
    ...

You probably want instanceof:

function House(roof, garage) {
    if (!(roof instanceof Roof) || !(garage instanceof Garage)) {
    ...

Answer 2

myRoof and myGarage are object types.

If you want to check if myRoof is an instance of Roof, use isinstanceof.

>>myRoof isinstanceof Roof
True

Answer 3

As noted by Richie, typeof will return 'object', not the name of the function. You should use the 'constructor' property. Use 'instanceof' operator.

Also, I have used two 'if statements' (instead of one, like you did) to throw different error message based on the particular error. This may mean a little more code, but when the code breaks, you know exactly what went wrong.

Working demo →

Code:

function Roof(type, material) {
     this.getType = function() { return type; }
     this.getMaterial = function() { return material; }
}

function Garage(numberOfCars) {
     this.getNumberOfCars = function() { return numberOfCars; }
}

function House(roof, garage) {
     if (roof instanceof Roof)
     {
        throw new Error('Argument roof is not of type Roof');
     }

     if(garage instanceof Garage) 
     {
          throw new Error('Argument garage must be of type Garage.');
     }

     this.getRoof = function() { return roof; }
     this.getGarage = function() { return garage; }
}

myRoof = new Roof("cross gabled", "wood");
myGarage = new Garage(3);
myHouse = new House(myRoof, myGarage);
alert(myHouse.getRoof().getType());