Ah Python, you have spoiled me for all other languages

[Ian Kelly]

On Fri, May 22, 2015 at 1:34 PM, MRAB <python at mrabarnett.plus.com> wrote:
> On 2015-05-22 20:14, Laura Creighton wrote:
>>
>> The first time you discover that in javascript typeof(null) is 'object'
>> and
>> not 'null' you will scream.  I wonder how many home versions of typeof
>> to replace the system one exist out in the wild?
>>
> I don't think that typeof(null) should be 'null'.
>
> If the type of an integer instance is the integer type and the type of
> a string instance is the string type, then the type of null should be
> the null type, not a null instance.
>
> I suppose that you could consider that what JavaScript is doing is
> equivalent to saying in Python that:
>
>     None = object()
>
> like you sometimes do when you want a unique sentinel because None
> itself would be an acceptable value.

If only it were that logical. null in Javascript is a primitive type.
Here's what typeof returns on some other primitive types:

js> typeof(4)
"number"
js> typeof(4.5)
"number"
js> typeof('hello')
"string"
js> typeof(true)
"boolean"
js> typeof(undefined)
"undefined"

An "object" in Javascript is basically just a collection of
properties. For example:

js> typeof([1, 2, 3])
"object"
js> typeof({a: 1, b: 2, c: 3})
"object"

Here's what happens when you try to access a property on null:

js> null.foo
typein:18:0 TypeError: null has no properties

We can conclude that null is not an object. Even the MDN reference
page for the typeof operator refers to this as "bogus". There was a
proposal to fix this in ECMAScript 5.1, but it was rejected because it
caused too much breakage.