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Ngan Kim Khong
Ngan Kim Khong

Posted on

Javascript true false weirdness

Recently I was trying to check true/false value for an object. I was pretty sure that an empty object is set to true in Javascript (as well as an empty array).
However, when comparing an empty object to true, I always get false.
Alt Text
This was spotted quite late into my Javascript journey, so I would like to share it here

Top comments (5)

eljayadobe profile image

The === equality check is a strong check. If something is truthy is does not necessarily equality-check to true.

Most everything in JavaScript is truthy. The 8 things that are falsy are:

  • false
  • 0
  • ""
  • null
  • undefined
  • -0 (I know, that's underhanded, but -0 is slightly different than 0)
  • NaN
  • document.all (in the HTML context)

Things that are truthy that occasionally mess people up:
var b = new Boolean(false)
var a = []
var o = {}

nk2303 profile image
Ngan Kim Khong

Thank you for the concept! Wow. It's really concise and simple, yet can give me great bugs if not careful :)

bias profile image
Tobias Nickel

and what is weired about it? I think it is super helpful. in the beginning I wrote something like this:

if (obj.prop !== undefined && obj.prop !== null) {

today I do

if (obj.prop) {

I think this is awesome.

and with the new optional chaining operator this get even better.

nk2303 profile image
Ngan Kim Khong

I was confused because if "an obj is true", then "obj === true" should return true, yet I got false. At least to my humanly logic, lol. I thought something wrong with my logic until I realized it was just the equal sign.

perpetualwar profile image
Srđan Međo

You need better understanding of truthy and falsy values in js... And what is object and what is boolean.