Best Way to Check 'Null', 'Undefined' or 'Empty' in JavaScript | JavaScript Tutorial for Beginners

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How to check if result is not 'Null', 'Undefined' or 'Empty' in JavaScript while using conditions? Lets discuss 'if not undefined, null or empty condition in javascript'. What is the best way to check if data is not null, not undefined and not empty in if else condition using JavaScript?

In JavaScript we display data or record if it exists, if it's not null, if it's not undefined and if it's not empty - otherwise we display a message, something like, 'no records found!'. Let's say we have data. We want to display this data, only if it's not empty, it's not undefined and not null. How can we do that easily? what is the best way of doing it?

There are several ways to check if data is null, undefined or empty but in conditions, we don't check that. Single line of code can check all these. Also, first handle the error, and in case of the error, stop code execution. In case of no error, proceed and show something.

If you are writing an if condition, you don’t need to check if something is empty or undefined or null.
It will automatically be considered as false. Javascript has a set of pre-defined falsy values.

Those are:

false
0 (zero)
'' or "" (empty string)
null
undefined
NaN (Not a Number)

So undefined, empty and null are falsy. If these are false, then, in 'if else condition' we only need to check if data is true or false. In case of true we proceed. In case of false we display error message.

So checking falsy or false is sufficient for 'undefined', 'empty' or 'null'. Do not check undefined, null or empty by using JavaScript 'comparison operators'. Check if the result is "falsy" (i.e., null, undefined, 0, '', false)

So this simple check is all you need to check whether data is undefined, null, empty or not any of these in JavaScript.

This is a common javascript interview question. So keep it mind as well.

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*Truthy Falsy Values in JavaScript*

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