Obj.toString() both equal to false and true?

Question

In a blank page on chrome console I type:

var o={};
o.toString() == false // false
o.toString() == true // false

I'm expecting o.toString to be evaluated as an empty string and so falsy...

What is happening?

Answer 1

Because {}.tostring() produces "[object Object]"

Your empty string assumption was incorrect and easily tested in a console

Answer 2

I'm expecting o.toString to be evaluated as an empty string and so falsy...

That expectation is at odds with the specified behavior of Object.prototype.toString (which is what ({}).toString is), which is to output "[object Object]" for plain objects.

So what you're doing is

"[object Object]" == true

(or == false ). If we follow the (convoluted) rules of the abstract equality comparison algorithm , that ends up being

Number("[object Object]") === Number(true)

...which is

NaN === 1

...which is false , because NaN isn't equal to anything.

Similarly

"[object Object]" == false

...ends up being

NaN === 0

...which is also false , because (again) NaN isn't equal to anything.

In a comment you've asked:

So why not truthy?

There's a big difference between coercing a value to boolean, like this:

if (o.toString()) {

...and comparing it to a boolean via == , like this:

if (o.toString() == true) {

They're just defined fundamentally differently, because == goes through a defined series of steps to try to make the values things it can compare, and it doesn't bias toward booleans when doing that (it biases toward numbers and strings).

Answer 3

It's because o={} and function toString return you "[object Object]"

If you need to get true / false if object is empty use something like:

ES5

var o1 = {};
if(Object.getOwnPropertyNames(o).length !== 0) console.log('true');
else console.log('false');

JQUERY: Check this: http://api.jquery.com/jQuery.isEmptyObject/

if($.isEmptyObject(o)) console.log('true');

Loadash :

if(_.isEmpty(o)) console.log('true');