更改 Javascript Object 的真/假值

Question

Basically can I do the following...

var obj = {}:
obj.falsey = true;
if(obj){
   //code not executed
}else{
   //code executed
}

I could take advantage of the fact ! , + , ~ ... Call valueOf/toString and do the following, but I would like to avoid that.

var obj = {valueOf:function(){return 0}}:
obj.falsey = true;
if(!!obj){
   //code not executed
}else{
   //code executed
}

Why would I want to do this? Because I'm curious:D

Answer 1

No, you can't. You have to implement some custom logic.

Answer 2

You can borrow a false Number , Boolean .... from an iframe and extend its prototype.

Basically the following doesn't work because Numbers are a primitive value.

var x = 0;
x.test = 'yo';
console.log(x.test);

This does, but obviously this pollutes the Number.prototype, so you should really borrow a different Number object from another iframe.

var x = 0;
Number.prototype.test = 'yo';
console.log(x.test);

Ultimately, just not a very good idea.

Answer 3

You can use loose equal to compare it to a boolean. People do that all the time, and finally it serves some purpose.

var obj = {valueOf: function() {return !this.falsey;}};
obj.falsey = true;
if (obj == true) {
   //code not executed
} else if (obj == false) {
   //code executed
}