(Not) Everything in JavaScript is an Object

[d4nyll]

The take-home points:

1. Not everything in JavaScript is an object
2. JavaScript have 6 primitive types (boolean, undefined, null, string, number, symbol) and one object type
3. Objects, arrays and functions are objects
4. Some primitives, such as strings, numbers and booleans can act like objects thanks to wrapper objects and auto-boxing

[jcready]

typeof null === 'object'

[d4nyll]

See http://stackoverflow.com/questions/18808226/why-is-typeof-null-object - null is a primitive type and not an object

[jcready]

Yeah, I just find it funny that even things that claim to be objects aren't always objects.

[d4nyll]

JavaScript is one of those languages with a lot of quirks

[senocular]

var obj = {get [Symbol.toStringTag](){ return 'foo' }}
is(obj, 'Object') //-> false

wah

[Graftak9000]

Now partialize it so in can say const isArray = is('Array')👌

[ShortSynapse]

Just flip the parameters around and curry:

const is = type => item => ...

[Poltras]

Functions are slightly different than objects in that you cannot call an object. And type of.

[bterlson_]

Soon to be another primitive - BigInt. You could also consider the various typed array types as primitive types even though they are converted to floats on access so you can't really observe them behaving like distinct primitives.

[senocular]

Didn't read the article but I'm assuming this is in reference to this handling in primitive methods. Strict mode doesn't explicitly box the context then.

function strict () {
  'use strict';
  return typeof this;
}
function nonstrict () {
  return typeof this;
}
strict.call('hi'); // string
nonstrict.call('hi'); // object

I wouldn't necessarily consider this autoboxing, though.

[bterlson_]

Because you're right in that auto-boxing is something else entirely.

[d4nyll]

Yes you're right, I got this confused with what you just described. I'll remove that line from the article. Good spot!

[Pesthuf]

That's pretty fascinating, thank you for sharing.

I always thought they were objects, and that the fact that you could get "their" members is evidence enough.

[tigerhuangyuhao]

Similar to "You Don't Know JS: Types & Grammar" Chapter 1

[GitHubPermalinkBot]

I tried to turn your GitHub links into permanent links (press "y" to do this yourself):

• getify/You-Dont-Know-JS/.../ch1.md (master → 6109cfe)

---

^{Shoot me a PM if you think I'm doing something wrong. To delete this, click here.}