Nullish Coalescing in JavaScript: A Developer’s Guide

Updated: February 14, 2024 By: Guest Contributor Post a comment

With the ever-evolving landscape of JavaScript, it’s crucial for developers to stay abreast of the latest features and enhancements that the language offers. One such feature, introduced in ECMAScript 2020 (ES11), is the Nullish Coalescing Operator (??). This powerful operator provides a more intuitive and cleaner way to deal with values that might be null or undefined. In this guide, we’ll dive deep into the nuances of Nullish Coalescing in JavaScript, enriched with various code examples to solidify your understanding.

Understanding Nullish Values

Before delving into Nullish Coalescing, it’s important to differentiate between JavaScript’s falsy values and nullish values. Falsy values include false, 0, -0, 0n, "" (empty string), null, undefined, and NaN. Among these, null and undefined are considered nullish, indicating the absence of any value.

What is Nullish Coalescing?

The Nullish Coalescing Operator (??) is a logical operator that returns its right-hand side operand when its left-hand side operand is either null or undefined, and otherwise returns its left-hand side operand. This is distinctly different from the JavaScript logical OR (||) operator, which returns the right-hand operand if the left-hand operand is any falsy value.

const greeting = user.greeting ?? 'Hello, stranger!'; console.log(greeting); // Output will be "Hello, stranger!" if user.greeting is null or undefined. 

Advantages of Nullish Coalescing

The principal benefit of using the Nullish Coalescing Operator is that it prevents JavaScript’s default behavior of coercing falsy values to false. This behavior can lead to unintuitive and often undesirable outcomes when working with variables that may legitimately hold falsy values like 0, false, or an empty string ("").

const isOnline = user.isOnline ?? true; console.log(isOnline); // Correctly outputs false if user.isOnline is explicitly set to false.

Practical Use Cases

Nullish Coalescing shines in scenarios where you need to set default values. Consider the example of setting a default greeting message:

const customGreeting = user.customGreeting ?? 'Welcome back!'; console.log(customGreeting);

This ensures that 'Welcome back!' is only used if user.customGreeting is null or undefined, not just any falsy value.

Combining with Optional Chaining

When used in conjunction with Optional Chaining (?.), Nullish Coalescing becomes even more potent, allowing developers to gracefully handle deeply nested objects:

const userLocation = userProfile?.location?.city ?? 'Location unknown'; console.log(userLocation);

This expression will output 'Location unknown' if either userProfile is null or undefined, or if userProfile.location or does not exist.


Nullish Coalescing in JavaScript offers a robust solution for handling null and undefined values explicitly, allowing for cleaner, more predictable code. By understanding and utilizing this operator, developers can avoid common pitfalls associated with falsy value coercion and ensure their applications handle variable states more gracefully. As JavaScript continues to evolve, features like Nullish Coalescing highlight the language’s commitment to developer productivity and code safety.

Experiment with the Nullish Coalescing Operator in your projects and observe how it can simplify your conditional logic and streamline your codebase. Embrace ES2020’s enhancements, and continue to explore the rich features JavaScript has to offer.