JavaScript inheritance with _.extend()

Question

Whats the difference between

Employee.prototype = Object.create(Person.prototype);

and

_.extend(Employee.prototype, Person.pr         


        

Answer 1

With Employee.prototype = Object.create(Person.prototype); you are completely replacing the Employee.prototype.

But with _.extend(Employee.prototype, Person.prototype); you are adding the Person.prototype on top of the Employee.prototype.

For example,

var a = {var1:1, var2:2};
var b = {var2:4, var3:3};
console.log(_.extend(a, b)); // {var1:1, var2:4, var3:3}

As you see, a it's not completely replaced by b, it's just extended by the properties defined in b.