Javascript constructor and prototype issue

Question

I have the following code which I am confused why when I define a prototype of property 'name' it comes out as '40' and not 'fred'? what is going on inside javascript? this seems like a simple question but one that I am confused about. Thanks!

function Product(id){
    this.id = id
    this.name = id + 20
}

Product.prototype.name = 'fred';
var p = new Product(20);
console.log(p.name);

Well, you set it to 40 inside the constructor - shadowing the value that would be inherited from the prototype. — Bergi
– Bergi, Commented Mar 12, 2014 at 12:38
thanks both of you, this seemed such an odd question when I posed it to myself as I don't normally get into a situation when I use the same name of a property on both the prototype of a constructor and within the constructor! thanks again. — quinton
– quinton, Commented Mar 14, 2014 at 16:19

xdazz · Accepted Answer · 2014-03-12 12:37:26Z

1

Because you did this.name = id + 20.

p.name will find the name property in the instance first, if not found, then try to find in the prototype.

function Product(id){
    this.id = id
}

Product.prototype.name = 'fred';
var p = new Product(20);
console.log(p.name); // then it will be fred

answered Mar 12, 2014 at 12:37

xdazz

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quinton Over a year ago

what is happening in javascript behind the scenes? can you explain please?

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