How Do I Check for Null Values in JavaScript?

In JavaScript, you can check for null values using various techniques. Here’s how you can do it:

1. Using the Strict Equality Operator (===)

To specifically check if a value is null, use the strict equality operator. This ensures that the value is exactly null and not undefined or another falsy value.

let value = null;

if (value === null) {
  console.log("The value is null");
}

2. Using the Loose Equality Operator (==)

The loose equality operator (==) also considers undefined equal to null. This is less precise and usually not recommended if you only want to check for null.

let value = null;

if (value == null) {
  console.log("The value is null or undefined");
}

3. Checking for Null in an Array

If you’re working with arrays, you can check for null values using array methods like filter, find, or includes.

let array = [1, null, 3];

if (array.includes(null)) {
  console.log("Array contains null values");
}

4. Using typeof (Not Recommended)

Using typeof directly won’t work for null because typeof null returns "object". This is a quirk in JavaScript.

console.log(typeof null); // Output: "object"

So, do not rely on typeof for null checks.

5. Combining with undefined Checks

If you want to check whether a variable is both defined and not null, combine the check:

let value = null;

if (value !== null && value !== undefined) {
  console.log("The value is neither null nor undefined");
} else {
  console.log("The value is null or undefined");
}

6. Checking with Optional Chaining

Optional chaining can help avoid errors when accessing deeply nested properties that might be null or undefined.

let obj = { a: null };

if (obj?.a === null) {
  console.log("The property 'a' is null");
}

Common Mistakes

• Confusing null with undefined: null means a variable is explicitly set to “no value,” while undefined means a variable has been declared but not assigned a value.
• Using typeof for null: As mentioned, typeof null returns "object", which can lead to confusion.