What is the best way to define dependent variables in an object?

Question

In the Google developers recommendation for optimizing JavaScript code, they mention that the best way to declare/initialize new variables for object is to use the prototype. For instance, instead of:

foo.Bar = function() {
this.prop1_ = 4;
this.prop2_ = true;
this.prop3_ = [];
this.prop4_ = 'blah';
};

Use:

foo.Bar = function() {
this.prop3_ = [];
};

foo.Bar.prototype.prop1_ = 4;
foo.Bar.prototype.prop2_ = true;
foo.Bar.prototype.prop4_ = 'blah';

However, in my case I have a dependency between variables, for instance:

var appv2 = function(){
this.start(this.person, this.car); 
}; 

appv2.prototype.toWhom = 'Mohamed'; 
appv2.prototype.person = new person(this.toWhom); 
appv2.prototype.car = new car();

appv2.prototype.start = function(person, car){
console.log('start for appv2 is called'); 
person.sayHello('me app v2');
car.brand();    
}; 

new appv2(); 

Using this.toWhom outside of the main constructor body or a method function of the object will yield undefined. To solve this I could use appv2.prototype.toWhom instead of this.toWhom or I could declare my dependent variables inside of the main constructor body.

But I would like to know what is the best way, in terms of performance, to accomplish this?

Thanks

Answer 1

To reference toWhom while creating person , you can either store the value in a separate variable:

var toWhom = appv2.prototype.toWhom = 'Mohamed';
appv2.prototype.person = new person(toWhom);

Or, reference it from the prototype , as you suspected:

appv2.prototype.person = new person(appv2.prototype.toWhom);

The reason this.toWhom is undefined is because this doesn't refer to an instance of appv2 there.