Javascript best practice to check only null values

Question

I want to check the null value in JavaScript.

For instance, test() is function which could return null. So If I want to test the null check efficiently what should be my approach.

var a = test();

followed by

if (a) {}

OR

if (a !== null) {}

? since if (a) will check for null, undefined, false, 0, NaN which might not be the best approach when we know we could get only null value.

Answer 1

To check null only

if (value !== null) {
}

If you want to check even for 'undefined'

if (typeof value !== 'undefined' && value !== null)

I will recommend you to check both undefined and null value.

function test() {
  var a;
  return a;  // returns undefined
}

function test() {
  var a = null;
  return a;  // returns null   
}

So there is a possibility that value can undefined or null. So better to check both.