JavaScript constructor parameter types

Question

I have a JavaScript class representing a car, which is constructed using two parameters, which represent the make and model of the car:

function Car(make, model) {
     this.getMake = function( ) { return make; }
     this.getModel = function( ) { return model; }
}

Is there a way to verify that the make and model supplied to the constructor are strings? For example, I want the user to be able to say,

myCar = new Car("Honda", "Civic");

But I don't want the user to be able to say,

myCar = new Car(4, 5.5);

Don't forget to declare to your variables.

kangax
– kangax

2009-10-11 06:38:34 +00:00
Commented Oct 11, 2009 at 6:38 — kangax
– kangax, Commented Oct 11, 2009 at 6:38

James · Accepted Answer · 2009-10-11 09:16:02Z

7

function Car(make, model) {
    if (typeof make !== 'string' || typeof model !== 'string') {
        throw new Error('Strings expected... blah');
    }
    this.getMake = function( ) { return make; };
    this.getModel = function( ) { return model; };
}

Or, just convert whatever you get to its string representation:

function Car(make, model) {
    make = String(make);
    model = String(model);
    this.getMake = function( ) { return make; };
    this.getModel = function( ) { return model; };
}

edited Oct 11, 2009 at 9:16

answered Oct 10, 2009 at 20:39

James

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1 Comment

kangax Over a year ago

It's usually better to use String(<smth>) instead of <smth>.toString(), since there's really no guarantee that an object has toString and that its toString is callable. I would also suggest to terminate function expressions with semicolons — to avoid any nasty behavior.

Hans Lawrenz · Accepted Answer · 2009-10-10 20:15:50Z

0

I think what you're looking for is the typeof operator. https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Operators/Special_Operators/typeof_Operator

answered Oct 10, 2009 at 20:15

Hans Lawrenz

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