Why Is Typeof Null "Object"

Why typeof (null) == 'object' in JavaScript?

It's been debated (see for example this discussion), and it's often seen as not really good, but it has a rationale : A null value takes the place of an object, it's the value you have when you expect an object and have none.

From ECMAScript :

null : primitive value that represents the intentional absence of any object value.

It's exactly the same as NaN being of type "number".

Why does typeof(null) return object , but you can't assign properties to it?

This page has a nice description of the history here surrounding why typeof(null) gives "object":

JS Data Types - Null

Here is the relevant portion (although I would suggest you read the whole post):

Why does typeof null return "object"?

// What's happening here?

typeof null === "object"; // true

The answer might disappoint some, but the truth is simply because the table above says to do so.

The reasoning behind this is that null, in contrast with undefined, was (and still is) often used where objects appear. In other words, null is often used to signify an empty reference to an object. When Brendan Eich created JavaScript, he followed the same paradigm, and it made sense (arguably) to return "object". In fact, the ECMAScript specification defines null as the primitive value that represents the intentional absence of any object value (ECMA-262, 11.4.11).

To draw a parallel here, consider typeof(NaN) === "number". So why does JavaScript give "number" as the type of NaN (not a number)? It is because NaN is used where numbers appear, it is a value that represents the intentional absence of a number value. Similar reasoning applies to null, the only difference being that null is implemented as a primitive and NaN is actually implemented as a Number object (so NaN.foo = 42 would actually work).

Why typeof null is 'object' in javascript?

typeof(null) returns "object"

and

 typeof('') returns "string"!

Why is null an object and what's the difference between null and undefined?

(name is undefined)

You: What is name? ^(*)

JavaScript: name? What's a name? I don't know what you're talking about. You haven't ever mentioned any name before. Are you seeing some other scripting language on the (client-)side?

name = null;

You: What is name?

JavaScript: I don't know.

In short; undefined is where no notion of the thing exists; it has no type, and it's never been referenced before in that scope; null is where the thing is known to exist, but it's not known what the value is.

One thing to remember is that null is not, conceptually, the same as false or "" or such, even if they equate after type casting, i.e.

name = false;

You: What is name?

JavaScript: Boolean false.

name = '';

You: What is name?

JavaScript: Empty string

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^{*: name in this context is meant as a variable which has never been defined. It could be any undefined variable, however, name is a property of just about any HTML form element. It goes way, way back and was instituted well before id. It is useful because ids must be unique but names do not have to be.}

Why null does not have a __proto__?

null in JS is considered as an object. typeof null == "object" //true

As already mentioned, null is actually a primitive value (like undefined, a Boolean value, a String value, a Number value, or a symbol) . But the language spec dictates that typeof null returns the string "object". (Similarly the specification dictates to return "function" for function objects instead of "object", like it does for array objects)

But that's only one half of the story.

Then why does null not have a __proto__

You might be wondering:

Why can I access the protoype of a string value ("foo".__proto__) but not null if both are primitive values ?

That's because Booleans, Strings and Numbers have object equivalents (e.g. new String("foo")) and when you try to access a property on a boolean/number/string primitive, they are internally converted to an object value

console.log("foo".slice)

// does `new String("foo").slice` internally

Detecting if object is null in Javascript - why doesn't this work?

For item = null, typeof item == "object" is true, so inside the block you're trying to access the classList property of a null value. You can't do that, hence the error.

To fix it, you're going to need another condition to stop null values from accessing the code.

if (typeof item == "object" && item != null)

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