How to Check if a Variable is Not NULL in JavaScript

In JavaScript, you often need to check if a variable is not null. This is a common task when you want to ensure that a variable has a meaningful value before proceeding with your code. Here’s how you can do it:

Basic Check for null#

To check if a variable is not null, you can use a simple !== (strict inequality) comparison:

if (variable !== null) {
    // variable is not null
}

Check for Both null and undefined#

Sometimes, you might want to check if a variable is neither null nor undefined. You can use the != (loose inequality) comparison for this purpose:

if (variable != null) {
    // variable is not null and not undefined
}

Note that != will return true for both null and undefined, which is usually desirable in cases where you want to handle both cases.

Using Logical Operators#

For more complex conditions, you might combine checks using logical operators. For example, if you want to ensure a variable is not null and also not an empty string:

if (variable !== null && variable !== "") {
    // variable is not null and not an empty string
}

Example#

Here’s a complete example showing how to check if a variable is not null:

function checkVariable(variable) {
    if (variable !== null) {
        console.log("The variable is not null.");
    } else {
        console.log("The variable is null.");
    }
}

let myVar = "Hello";
checkVariable(myVar); // Output: The variable is not null.

myVar = null;
checkVariable(myVar); // Output: The variable is null.

Summary#

• Use variable !== null to check if a variable is not null.
• Use variable != null to check if a variable is neither null nor undefined.
• Combine conditions with logical operators if needed to handle more complex cases.

Feel free to adapt these methods to fit the needs of your specific application!