When is a variable's data type in javascript `Null`?

Question

Is it actually possible to get the Null data type as a return from the typeof function - if so what case yields that result, when is a variable actually of the Null type?

    typeof myVAR; //gives me "undefined" before the variable declaration

    var myVAR;
    typeof myVAR; //also gives me "undefined"

    myVAR = null; //assigned the null object
    typeof myVAR; //gives me "Object" (which I guess makes sense because `null` is an object and that's what I assigned to the variable)

possible duplicate of Why is null an object and what's the difference between null and undefined? — PSL
– PSL, Commented Oct 15, 2013 at 0:18
@PSL not quite, that explains what the null value is - but my question is geared more towards Null (the data type)? — Suvi Vignarajah
– Suvi Vignarajah, Commented Oct 15, 2013 at 1:46

Qantas 94 Heavy · Accepted Answer · 2013-10-15 00:27:52Z

8

typeof never returns "null", but there is an internal null type:

Typeof Results:

Undefined: "undefined"
Null: "object"
Boolean: "boolean"
Number: "number"
String: "string"
Object (native and does not implement [[Call]]): "object"
Object (native or host and does implement [[Call]]): "function"
Object (host and does not implement [[Call]]): Implementation-defined except may not be "undefined", "boolean", "number", or "string".

The only way to test for null would be a direct comparison with the null value, using the === operator.

edited Oct 15, 2013 at 0:27

answered Oct 15, 2013 at 0:19

Qantas 94 Heavy

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5 Comments

Suvi Vignarajah Over a year ago

hmm..thank you, that answers part of my question, but can a variable ever be of Null data type?

Qantas 94 Heavy Over a year ago

@SuviVignarajah: A variable can have the null value, which is the only value of the Null data type.

Suvi Vignarajah Over a year ago

I understand now - I did some research, seems like the Undefined data types "special" value is also undefined (similar to Null and null). You can declare a variable var myVAR = undefined, and typeof myVAR will yield undefined still. Seems like the typeof in javascript just doesn't return Null or null as one of the types like you state in your answer.

Qantas 94 Heavy Over a year ago

@SuviVignarajah: typeof doesn't return the actual name of the internal type - that may be slightly confusing.

Suvi Vignarajah Over a year ago

Slightly..on another note, this explanation here gives me some closure though about why typeof null yields "object".

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