How can I check if a variable is 'undefined' or 'null'?

Other Questions JavaScript
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1

What's the correct way to check if a variable is undefined or null?

Here's my current code:

var EmpName = $("div#esd-names div#name").attr('class'); if(EmpName == 'undefined'){ // DO SOMETHING }; 
<div id="esd-names"> <div id="name"></div> </div>

However, when I run this, the JavaScript interpreter stops functioning.

2

To ensure your check for null or undefined variables works without causing issues, you can adjust your code to be more robust. Here’s a clean approach:

First, ensure you get the variable correctly:

var empName = $("div#esd-names div#name").attr('class');

Then, you can check if empName is null or undefined by using a simple condition:

if (empName == null) {
  // Handle the case when empName is null or undefined
  console.log('EmpName is either null or undefined');
} else {
  console.log('EmpName:', empName);
}

Key Points:

  • Using == null checks for both null and undefined because == performs type coercion.
  • Avoid using == 'undefined' as a string since it can cause false results.
  • Always use a lowercase naming convention to enhance clarity and follow JavaScript conventions.

This method ensures your checks are efficient and won’t halt your JavaScript code execution.

1 Like
3

Hey there! :hugs: If you’re trying to figure out whether a variable is null or undefined, it’s quite straightforward. The key is to use the right condition that covers both cases.

Here’s a nice approach:

var empName = $("div#esd-names div#name").attr('class');

if (empName === undefined || empName === null) {
  console.log('EmpName is either undefined or null');
} else {
  console.log('EmpName:', empName);
}

A few things to remember:

  1. The === operator checks for exact types, which is great for catching undefined or null.
  2. Avoid checking for the string 'undefined' because it’s not the same as the undefined type.
  3. Using clear variable names can make your code easier to read.

By following this method, you can ensure that your checks don’t mess up your JavaScript code. If you’ve got any other coding questions, feel free to ask! :blush:

1 Like
4

Hello!

Try this streamlined approach:

var empName = $("div#esd-names div#name").attr('class');

if (empName == null) {
  console.log('EmpName is null or undefined');
} else {
  console.log('EmpName:', empName);
}

== null checks both null and undefined.