Is there a better way to check if variable is null value or not in JavaScript?

[SunilK Chauhan]

Hi,

I am using only below way to check if variable is null or not.
But is there any better to check in node js?

var a = '' ;
if (a == '') {}

[Stephan van Hulst]

Your code doesn't check that a is null. It's possible to assign certain values to a so that your condition will evaluate to true anyway, the most obvious of which you have demonstrated yourself by assigning the empty string to a.

There are three approaches you can take, depending on what a represents and what you want your application to do with it:

1) Check that a is exactly null: if (a === null) {

2) Check that a is similar to null: if (a == null) {

3) Check that a is falsey: if (!a) {

The most common approach is the third.

[Cay Horstmann]

It may be that the most common approach is to check if (!a), but it does not mean that it is a good approach.

That test also passes if a is 0 or "", which can really bite you if that's not what you expect.

If you write what you mean, your code will work and it will be comprehensible. If you need to check for null, the best solution is if (a === null).

Cheers,

Cay

[Bear Bibeault]

Cay Horstmann wrote:That test also passes if a is 0 or "", which can really bite you if that's not what you expect.

I have scars to show for that one...

To add another twist to the discussion: frequently null (or undefined) is checked for in order to provide a default if a value is null/undefined. A very recent addition (check your environment for compatibility) is called nullish coalescing and goes like so:

a ?? b

whose value is a if a is not null and not undefined, b otherwise.

This is nice because it avoids the zero and empty string pitfalls that Cay pointed out.

[SunilK Chauhan]

Ok thanks.