4 Best way to check Undefined or Null in JavaScript

JavaScript is a dynamically-typed language, which means that variables can hold values of different types at different points in time. However, this flexibility can also lead to some challenges, especially when it comes to dealing with null or undefined values. Fortunately, there are several reliable ways to check for null or undefined values in JavaScript, each with its own strengths and weaknesses. In this article, we'll explore four of the best ways to check for null or undefined values in JavaScript, and discuss when each method is most appropriate.

1. Using the typeof operator

The typeof operator returns a string indicating the type of the operand. If a variable is undefined, the typeof operator will return the string "undefined". Similarly, if a variable is null, the typeof operator will return the string "object". Here's an example:

One potential drawback of using the typeof operator to check for undefined values is that it will also return "undefined" for undeclared variables. In other words, if you try to check the type of a variable that has not been declared, the typeof operator will still return "undefined", even though the variable does not exist.

2. Using the strict equality operator (===)

The strict equality operator (===) checks if two values are equal in value and type. If a variable is null or undefined, it will be strictly equal to null or undefined, respectively. Here's an example:

One potential drawback of using the strict equality operator to check for null or undefined values is that it will not catch cases where a variable is "falsy" but not strictly equal to null or undefined. For example, if a variable is an empty string or the number 0, it will not be caught by this method.

3. Using the nullish coalescing operator (??)

The nullish coalescing operator (??) returns the value of its left-hand side operand if it is not null or undefined; otherwise, it returns the value of its right-hand side operand. Here's an example:

One potential drawback of using the nullish coalescing operator is that it is a relatively new addition to the language, so older browsers may not support it.

4. Using the optional chaining operator (?.)

The optional chaining operator (?.) allows you to access nested properties of an object without throwing an error if any of the properties in the chain are null or undefined. Here's an example:

One potential drawback of using the optional chaining operator is that it is also a relatively new addition to the language, so older browsers may not support it.

In general, each of these methods has its own strengths and weaknesses, so choose the method that best fits your use case. It's also worth noting that there are many other ways to check for undefined or null values in JavaScript, so don't be afraid to explore and experiment with different approaches.