Attribution operator "=" javascript

Question

I’ll tell you what:

var d = new Date();
var dataInicial = new Date(2017, 5, 1);
var dataFinal = new Date(2017, 5, 20);

var percorreDatas = function(){
  d = dataInicial;
  while(d <= dataFinal){
    d.setDate(d.getDate()+1);
    console.log("d", d);
    console.log("dataInicial", dataInicial);
  }
}

percorreDatas();

Why is the variable "starting date" updating along with the variable "d", if I don’t increment it??????

Answer 1

As @Guilhere Nascimento commented, this is because objects in Java are mere references to a memory position.

var d = new Date();
var dataInicial = new Date(2017, 5, 1);
var dataFinal = new Date(2017, 5, 20);

For example, let’s say the variable

• d is stored at position 01.
• dataInicial at position 02.
• dataFinal at position 03.

When you define that d = dataInicial, the variable d no longer points to position 01 of memory, but to position 02, which is the position occupied by the variable dataInicial.

When you do d.setDate(d.getDate()+1), as strange as it may seem ,you are updating the 02 position of memory, not the 01 position, which is where the variable d was allocated initially.

At this point, there are two variables, d and dataInicial, which, although they have different names, will always have the same value, since both point to the same memory position.