Question

Considering the simplistic scenario:

 function Base() {} function Child() {} Child.prototype = new Base; 

I wonder why would an instance of Child have constructor property set to Base and not to Child?

Answer 1

It’s all tied to how inheritance works in JavaScript. Check this link for a detailed explanation (basically, constructor is just another property of the prototype).

Edit: Also, if you want ‘real’ prototypical inheritance, you have to use some sort of clone function, eg

function clone(obj) {     if(typeof obj !== 'undefined') {         arguments.callee.prototype = Object(obj);         return new arguments.callee;     } } 

Then, you can do things like this

function Base() {} function Sub() {} Sub.prototype = clone(Base.prototype);  var obj = new Sub; 

and you’ll still get true two times on

document.writeln(obj instanceof Sub); document.writeln(obj instanceof Base); 

The difference to your solution is that Base() won’t be called and Sub.prototype will only inherit the properties of Base.prototype – and not the ones set in the constructor.