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Code And Deploy
Code And Deploy

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How To Check Empty, Null, and Undefined Variables in Javascript / jQuery?

Originally posted @ https://codeanddeploy.com visit and download the sample code: https://codeanddeploy.com/blog/jquery/how-to-check-empty-null-and-undefined-variables-in-javascript-jquery

In this post, I will share a basic code in Javascript/jQuery that checks the empty, null, and undefined variables. If you using javascript/jquery usually you need to check if the variable given is not empty, nulled, or undefined before using it to your function. Because if you don't validate your variables it could cause an error to your javascript code.

Check empty variable

In this example, I have an if statement in javascript that will check the variable is empty.

var a = '';

if(a == ''){
  console.log('Empty');
}
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Check null variable

In this example, it will check the nulled variable before executing it.

var a = 'codeanddeploy';

if(a == null || a == NULL){
  console.log('Nulled');
}

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Check undefined variable

As you can see below, I used typeof() function in javascript to determine variable data type.

if(typeof a == "undefined"){
   console.log('undefined');
}
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I hope this tutorial can help you. Kindly visit here https://codeanddeploy.com/blog/jquery/how-to-check-empty-null-and-undefined-variables-in-javascript-jquery if you want to download this code.

Happy coding :)

Top comments (4)

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fjones profile image
FJones • Edited on

Going off the top of my head, but I might be missing a few idiosyncracies of JS (like operand order, lol)

  1. Use strict comparison operators. == '' does not work for, e.g. [], but will work for false and "".
  2. NULL doesn't exist, but may at best be an alias for null, making that a redundant or broken condition.
  3. This is a bit contentious, but I would generally advise typeof undefined over "undefined".
  4. This is missing a lot of falsey values to check for, and particular ways of checking for them.
  5. God knows what this is supposed to have to do with jQuery.
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jonrandy profile image
Jon Randy 🎖️ • Edited on

Your 'check null variable' code does not work - will cause an error. It also demonstrates a lack of knowledge of JS

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curiousdev profile image
CuriousDev

The first check is for an empty string. I am not aware of something like "NULL". Also let me add, that for checking for undefined or null you can just write the variable without anything else in the brackets of the condition, like "if (variable) ...". Please correct wrong points in case these are given and also have a look at the linked articles, which can have the same issues.

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chriskt profile image
chris

You're also checking to see if the variable is equal to the string value "undefined". I'm sorry, but this is a very poor post and should be avoided.

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