Delete

Execute this code:

var name = 'John',
    obj = {
        name: 'James'
    },
    Animal,
    mammal;

Animal = function(){};
Animal.prototype.name = 'animal';

mammal = new Animal();
mammal.name = 'mammal';

delete name;

console.log('#1: ' + name);

delete obj.name;

console.log('#2: ' + obj.name);

delete obj.toString;

console.log('#3: ' + obj.toString);

delete mammal.name;

console.log('#4: ' + mammal.name);

The execution of this code logs:

#1: John

#2: undefined

#3: function toString() { [native code] }

#4: animal

Why #1: John is logged?

John is logged because name is a global variable and global variables can't be deleted.

__match_answer_and_solution__

Why #2: undefined is logged?

undefined is logged because we have deleted the name property of obj, properties or members of objects can be deleted excluding the properties or members of the global object.

__match_answer_and_solution__

Why #3: function toString() { [native code] } is logged?

function toString() { [native code] } is logged because toString is an inherited method from Object and inherited methods or members can't be deleted.

__match_answer_and_solution__

Why #4: animal is logged?

animal is logged because we have deleted the own mammal.name property but the inherited property is shown.

__match_answer_and_solution__