Can an Object be false?

Question

Is there any way to make an object return false in javascript?

var obj = new Object();

console.log(!!obj) // prints \"true\" even if it\'s empty
         


        

Answer 1

We can overwrite Object.prototype.valueOf to make an object appear to be false when it is coerced into a primitive, for example during ==.

However it will not appear to be false when we force it into a boolean using !!, so it doesn't really work in the general case.

var obj = {
    valueOf: function () {
        return false
    }
}

> obj == false
true               // Good, we fooled them!

> !!obj
true               // Not so good, we wanted false here

> Boolean(obj)
true               // Not so good, we wanted false here