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

No. But null will convert to false.

> typeof(null)
"object"
> null instanceof Object
false
> !!null
false

To see if the object contains any properties, use (shamelessly copied from http://stackoverflow.com/questions/1345939/how-do-i-count-javascript-objects-attributes):

function isEmpty (obj) {
    for (var k in obj) 
       if (obj.hasOwnProperty(k))
           return false;
    return true;
}

Answer 2

A null "object" (really value) will return false.

var obj = null;

console.log(!!obj);

If you wanted to check if it has no properties, you might try:

var obj = new Object();
var empty = true;
for (var p in obj) {
    if (obj.hasOwnProperty(p)) {
       empty = false;
       break;
    }
}
console.log(empty);

Answer 3

I think that with the first ! you are casting obj to a boolean and negating its value- resulting in true if obj is null - , and with the second ! negating it again.

Answer 4

No. An object that doesn't have any properties assigned is not considered "empty".

The fact that a variable holds an instance of an object is enough to cause javascript to treat the variable as having the value of true when an expression requires a boolean value.

Edit

There are clearly some nuances to be cleared up looking at the other answers here.

null is not an object, it is the distinct lack of an object. The question refers to an Object, that is one that has just been created.

Answer 5

No.

Not sure why you'd want this, but there is a way you could do something like this but it's kinda hacky...

var obj = {
    toString: function() { return ''; }
};

alert(!! (''+obj));