Why in changeName statement we use only function (name) and not person (name) ?

Question

function person(name, age) {
this.name = name;
this.age = age;
this.changeName = function (name) {
this.name = name;
}
}

var p = new person("David", 21);
p.changeName("John");

Answer 1

Firstly, function(name) { this.lastname = name; } is a function expression.

Thus, the function is originally stored in a constructor-local variable. By storing it in a property of this, it become a method of the constructed object, instead of just a function that is local to the constructor.