why using NULL with logical operator throws error in JS

Question

This is the code I am testing --

Works fine

document.write( 1 && undefined ); // prints undefined
document.write( 1 && 3 ); // prints 3 
document.write( 1 && true ); // prints  true

Throws error

document.write( 1 && NULL ); // throws Error

why using NULL throws arror although its working even for undefined

although i tested typeof NULL and its giving undefined but still its not working.let me know about this. (New to OOP programming)

@Trailcoder can u try document.write( 1 && null ); – rab Mar 22 '13 at 07:01 — rab, Mar 22 '13 at 07:01
Add this to make it work: `var NULL = null;` – Ja͢ck Mar 22 '13 at 07:04 — Ja͢ck, Mar 22 '13 at 07:04

rab · Accepted Answer · 2013-03-22T07:11:57.393

4

NULL does not exist, try this

try {
    document.write( 1 &&  NULL  );
} catch ( e) {
    document.write( 1 &&  null  );
}

edited Mar 22 '13 at 07:11

answered Mar 22 '13 at 07:05

rab

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score 1 · Answer 2 · answered Mar 22 '13 at 07:03

1

NULL is undefined because it doesn't exist. You're thinking of null.

answered Mar 22 '13 at 07:03

Hubro

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score 1 · Answer 3 · answered Mar 22 '13 at 07:03

1

document.write(1 && null); outputs null.

NULL does not exist in JavaScript because it's case-sensitive. It must be null.

answered Mar 22 '13 at 07:03

Matías Fidemraizer

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score 0 · Answer 4 · answered Mar 22 '13 at 07:04

0

It's null (lowercase), not NULL (uppercase)

answered Mar 22 '13 at 07:04

ulentini

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score 0 · Answer 5 · answered Mar 22 '13 at 07:04

0

Because undefined is different to a symbol that doesn't exist, the browser is throwing an error. From the Chrome console:

> 1 && null
null
> 1 && NULL
ReferenceError: NULL is not defined
> NULL
ReferenceError: NULL is not defined

answered Mar 22 '13 at 07:04

Daniel Imms

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score 0 · Answer 6 · answered Mar 22 '13 at 07:07

0

read this may be it will answer your question JavaScript undefined vs. null

answered Mar 22 '13 at 07:07

Nasir Mahmood

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score 0 · Answer 7 · answered Mar 22 '13 at 07:08

Using typeof something only gives the type of that expression; it's undefined in this case and so using that symbol naturally gives an error. It's the same as:

typeof unknownvar
// "undefined"
unknownvar
// ReferenceError: unknownvar is not defined

The exception is the symbol undefined itself:

typeof undefined
// "undefined"
undefined
// undefined

In your particular case, NULL should be null.

why using NULL with logical operator throws error in JS

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