others-How to check null/empty/undefined/NaN with javascript(js)

1. Purpose

In this post, I would demo how to check where a variable is null / empty / undefined /NaN with javascript or js.

2. The solution

2.1 Check for null

TL;DR Here is the final solution to check for null in javascript(js):

if (variable === null)

This test will ONLY return true for null and will return false for "", undefined, false, 0, or NaN.

e.g.

if (variable === null)

- variable = ""; (false) typeof variable = string

- variable = null; (true) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (false) typeof variable = number

This test would return true only if the variable is null.

2.2 Check for empty

TL;DR Here is the final solution to check for empty in javascript(js):

if (variable === '')

This test will ONLY return true for '' and will return false for null, undefined, false, 0, or NaN.

e.g.

Empty String Test:

if (variable === '')

- variable = ''; (true) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (false) typeof variable = number

2.3 Check for undefined

TL;DR Here is the final solution to check for undefined in javascript(js):

if (typeof variable == "undefined")

-- or --

if (variable === undefined)

This test will ONLY return true for undefined and will return false for '', false, 0, or NaN. e.g.

Undefined Test:

if (typeof variable == "undefined")

-- or --

if (variable === undefined)

- variable = ''; (false) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (true) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (false) typeof variable = number

2.4 Check for NaN

TL;DR Here is the final solution to check for NaN in javascript(js):

if (typeof variable == 'number' && !parseFloat(variable) && variable !== 0)

-- or --

if (isNaN(variable))

This test will ONLY return true for NaN and will return false for '',null, undefined, false, 0. e.g.

NaN Test:

if (typeof variable == 'number' && !parseFloat(variable) && variable !== 0)

-- or --

if (isNaN(variable))

- variable = ''; (false) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (true) typeof variable = number

2.5 Always use === instead of ==

Because:

`==` is a loose or abstract equality comparison

`===` is a strict equality comparison

See the MDN article on Equality comparisons and sameness for more detail.

image-20211129160615525

image-20211129160601154

3. Summary

In this post, I demonstrated how to use javascript === to compare variable with null/empty/NaN/undefined etc, the key point is to use === instead of ==, because === is more strict than ==. That’s it, thanks for your reading.

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