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Discussion on: What is the oddest JavaScript behavior?

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Replies for: It's not insane. null, like nil in ruby, a singleton instance of NilClass is technically an object. Technically an array is also an object, which ...

 
willsmart profile image
willsmart • • Edited

But at least ruby is rigorously consistent OO like that.

irb(main):004:0> nil.methods
=> [:&, :^, :|, :===, :inspect, :to_a, :to_s, :to_i, :to_f, :nil?, :to_h, :to_r, :rationalize, :to_c, :tap, :public_send, :instance_variables, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :private_methods, :kind_of?, :is_a?, :instance_variable_get, :method, :public_method, :singleton_method, :instance_of?, :extend, :define_singleton_method, :to_enum, :enum_for, :<=>, :=~, :!~, :eql?, :respond_to?, :freeze, :object_id, :display, :send, :hash, :class, :singleton_class, :clone, :dup, :itself, :taint, :tainted?, :untaint, :untrust, :trust, :untrusted?, :methods, :protected_methods, :frozen?, :public_methods, :singleton_methods, :!, :==, :!=, :__send__, :equal?, :instance_eval, :instance_exec, :__id__]

In JS there are very few object-type calls that work in any way with nulls, so it's neat that they aimed to make this aspect of the language more OO, but they should have followed through better.
typeof(null) being 'object' is seldom anything but annoying for JS devs.

eg.

> Object.getOwnPropertyNames(null)
< Uncaught TypeError: Cannot convert undefined or null to object
    at Function.getOwnPropertyNames (<anonymous>)
    at <anonymous>:1:8
> null.foo
< Uncaught TypeError: Cannot read property 'foo' of null
    at <anonymous>:1:6
(anonymous) @ VM176:1
> for (const k of null);
< Uncaught TypeError: null is not iterable
    at <anonymous>:1:17

Basically there are very few times you might write typeof(thing)==='object' where you shouldn't do the null check too

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sleeplessbyte profile image
Derk-Jan Karrenbeld •

Absolutely true. I was only referring to the use of the word "insane" which just sounds very unknowing/ignorant to me.

FWIW, now that we use TS for most things, this is not problem for us often, except for when something is nullable ánd multiple types (object/number/string/undefined).

My recommendation is to never use null and only use undefined. Replace your "null"s with an "EMPTY/UN_SET" data type.

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willsmart profile image
willsmart •

Fair enough. I didn't mean insane in the sense of completely without reason, just in the sense that it was badly thought out.

The thing is that nulls are now baked into JS at a few levels, so in our own code we can avoid them, but they pop up throughout the various JS apis, eg

> /a/.exec('b')
< null
> document.body.getAttribute('a')
< null

That's what I mean by the loose "insane" comment. It was a mistake that was bad enough that as JS devs we're now best off to generally avoid the fundamental null value in JS.

I totally agree with you about TS, which corrects many of these issues, and how in JS we're best to use undefined whereever possible.