Object must return function

Question

I have some JS code here:

function Car(manufacturer, model, year) {
    this.manufacturer = manufacturer;
    this.model = model;
    this.year = year == undefined ? new Date().getFullYear() : year;
    this.getInfo = function(){
        return this.manufacturer +' '+ this.model +' '+ this.year;
    };
}

var bmw = new Car("BMW", "X5", 2010);

So I want some interesting output in the console:

console.log('Car: ' + bmw); // Car: BMW X5 2010

How to do it without calling any methods?

THANKS!

I need the 'getInfo' method, so I have simply changed my code:
function Car(manufacturer, model, year) {
    this.manufacturer = manufacturer;
    this.model = model;
    this.year = year == undefined ? new Date().getFullYear() : year;
    this.toString = this.getInfo = function(){
        return this.manufacturer +' '+ this.model +' '+ this.year;
    };
}

Greg · Accepted Answer · 2012-08-23 11:23:18Z

console.log just outputs to the console what it is given as a parameter. In your case, you are giving it a string (by concatenating a string with an object).

If you were to simply put console.log(bmw) you would see an interesting outcome - depending on which web inspector you are using, you will be able to click through all of bmw's properties... very nice.

The representation of console.log(bmw) in Chrome Developer Tools:

enter image description here

To answer your precise question, you can change the string representation of an object by overriding its toString() function.

function Car(manufacturer, model, year) {
    this.manufacturer = manufacturer;
    this.model = model;
    this.year = year == undefined ? new Date().getFullYear() : year;
    this.getInfo = function(){
        return this.manufacturer +' '+ this.model +' '+ this.year;
    };

    // Build the string up as you wish it to be represented.
    this.toString = function() {
        var str = this.manufacturer + " " + this.model + " " + this.year;
        return str;
    };
}

var bmw = new Car("BMW", "X5", 2010);
console.log('Car: ' + bmw); // Car: BMW X5 2010

Frédéric Hamidi · Accepted Answer · 2012-08-23 11:20:33Z

0

You can override your object's toString() method:

function Car(manufacturer, model, year) {
    this.manufacturer = manufacturer;
    this.model = model;
    this.year = year == undefined ? new Date().getFullYear() : year;
    this.toString = function() {
        return this.manufacturer + ' ' + this.model + ' ' + this.year;
    };
}

You can test the results in this fiddle.

answered Aug 23, 2012 at 11:20

Frédéric Hamidi

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3 Comments

Nikita Shekhov Over a year ago

So as I understood the 'toString' method is called each time I call an object?

Denys Séguret Over a year ago

No : only when a string representation is needed. "somestring"+aobject is an example of such occurence.

Denys Séguret Over a year ago

@FrédéricHamidi I'll remove the comment but I'm not the downvoter

Denys Séguret · Accepted Answer · 2012-08-23 11:27:32Z

0

You may override the toString method :

Car.prototype.toString = function() {
    return this.model + ' ' + this.year;
};

This method is automatically called when a string representation of the object is needed (for example when you do "somestring" + yourObject.

Reference : https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Object/toString

edited Aug 23, 2012 at 11:27

answered Aug 23, 2012 at 11:20

Denys Séguret

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