Is it always possible that (a == 1 && a == 2 && a == 3) can be evaluated as true in JavaScript?

It is possible if a is a constant object that returns values that are incremented each time the object is invoked. In the case below:

const a={
  valor: 1,
  valueOf: function(){
    return a.valor++;
  }
}

On the first invocation of a it will return 1 . After this, every time% w_ of% is called, it will return the last value a (1, 2, 3 ...).

Therefore,% w_ of% will be true, because w_% will be equal to 1, 2, and 3 returned from the% w_% constant.

When I invoke +1 , the value of (a == 1 && a == 2 && a == 3) is a (true) and a becomes value a == 1 , so a is also true, and so on

For example, you could do that too the result is the same:

const a={
   valor: 1,
   valueOf: function(){
      return a.valor++;
   }
}  

if(a == 1 && a == 2 && a == 3 && a == 4 && a == 5){
    // até esse "a" no console.log abaixo já incrementa o valor
    console.log("fim. O valor de a é "+a); 
}

There is a similar question in SOen .