Javascript Array push Object by reference

Let's have a look at what is happening:

var abc = { a: 10, b: 20};

A new object is created in memory and assigned to the variable abc.

var def = [];

A new array is created in memory and assigned to the variable def.

def.push(abc);

Inside the array there is now a pointer to the formerly created object.

abc.a = 100;
def[0].a; // outputs 100!

Obviously right. We are modifying the object, which is also referenced by the array.

abc = { a: 10000, b: 20000 };

Again a new object is created and a reference to it is stored in abc. Now we have two objects (and an array) in memory.

def[0].a; // still 100, no change this time

Of course, this is still 100. The array pointer still references the first created object and not the second one.