Unleash the Power of JavaScript Double Question Marks: Learn How to Implement Them with These Code Examples

Table of content

  1. Introduction
  2. What are Double Question Marks?
  3. Why Use Double Question Marks?
  4. Basic Syntax of Double Question Marks
  5. Code Examples
  6. Conclusion


JavaScript, a high-level, dynamic programming language used to create interactive web pages and web applications, has undergone numerous upgrades and improvements over the years. With the release of ECMAScript 2020, or ES2020, developers were introduced to a new feature called the nullish coalescing operator, also known as double question marks (??). This feature allows for more concise and efficient code, which can lead to better performance, easier debugging, and improved readability.

In this article, we will explore the basics of JavaScript's double question marks and how they can be implemented in your code. From understanding how they differ from the logical OR operator to seeing practical examples of how they can be useful in different contexts, we aim to provide you with a thorough to this new feature. Whether you're a seasoned JavaScript developer or just starting out, understanding double question marks and how to use them is a valuable skill to have in your arsenal. So, let's dive in and unleash the power of JavaScript double question marks!

What are Double Question Marks?

Double Question Marks are a new feature introduced in ECMAScript 2020 that offer developers a simpler way to handle nullish values in JavaScript. This operator, denoted by ??, allows programmers to check for values that are either null or undefined, and provide a default value in case of these nullish values. This syntax provides a significant convenience in cases where default values need to be provided for nullish coalescing expressions.

When implementing Double Question Marks, it's important to note that the operator only considers nullish values, which include null and undefined, but not falsy values such as empty strings, the number 0, or false Boolean values. This feature can greatly simplify code by allowing developers to avoid using conditional statements or ternary operators that would otherwise be required to achieve nullish coalescing.

One major advantage of Double Question Marks is that it reduces the likelihood of bugs in code, as it provides a more reliable way to handle nullish values. For example, in older versions of JavaScript, a default value might be set as 0, which could cause bugs if the actual value was also 0. With Double Question Marks, developers can easily set a default value that is distinct from the nullish value, which greatly reduces the potential for bugs in code.

Overall, the addition of Double Question Marks to JavaScript provides developers with a simpler, more reliable way to handle nullish values, making code easier to read, write, and maintain. By using Double Question Marks, developers can ensure their code is more efficient, and easier to debug and maintain over time.

Why Use Double Question Marks?

Double question marks, also known as the nullish coalescing operator, are a new feature in JavaScript that allows developers to quickly and easily check whether a variable is null or undefined without having to write complex if statements or use the ternary operator. This new operator is extremely useful in scenarios where there may be a default value that needs to be returned if a variable is null or undefined. The double question mark operator is especially helpful when dealing with APIs that return null or undefined values.

Using the double question mark operator in JavaScript is also a more efficient way to check for null or undefined values. Previously, developers have had to use the || (OR) operator to achieve the same result. However, this could lead to errors when the default value is a falsy value such as 0 or an empty string. Using the double question mark operator ensures that only nullish values are replaced with the default value.

It's important to note that the double question mark operator is still relatively new and may not be supported by all browsers or versions of JavaScript. However, with its many benefits and growing popularity, it's likely to become a standard part of the language in the near future. So, for developers looking to improve their code efficiency and avoid common null and undefined errors, integrating double question marks into their JavaScript projects is highly recommended.

Basic Syntax of Double Question Marks

The double question mark (??) is a recent addition to JavaScript's syntax that allows for more concise and streamlined coding. The syntax for the double question mark is simple: it checks if the value on the left is nullish (either null or undefined) and if so, it returns the value on the right. Otherwise, it returns the value on the left.

Here's an example of how the double question mark works:

const example1 = null ?? "hello world";
console.log(example1); // "hello world"

const example2 = "goodbye" ?? "hello world";
console.log(example2); // "goodbye"

In this code snippet, the first example uses the double question mark to check if the value of example1 is nullish. Since it is, it returns the value on the right, which is "hello world". The second example checks if the value of example2 is nullish. Since it's not, it returns the value on the left, which is "goodbye".

The double question mark can be a useful shorthand for writing code that needs to handle nullish values in a concise way. It's a clear improvement over older methods, such as using a ternary operator or if statements to check for nullish values.

In the next section, we'll explore some more advanced uses of the double question mark and see how it can be used in more complex code.

Code Examples


Double question marks are a powerful feature in JavaScript that allow for concise and efficient error handling. With the introduction of nullish coalescing in the ES2020 update, the double question mark operator has become even more useful. Here are some to help you implement this feature in your own JavaScript code:

1. Basic Usage:

let x;
let y = x ?? 'default';
console.log(y); // Output: 'default'

In this example, y is assigned the value of x if it is not null or undefined. Otherwise, it is assigned the value 'default'. This code is equivalent to the following:

let x;
let y;
if (x !== null && x !== undefined) {
  y = x;
} else {
  y = 'default';
console.log(y); // Output: 'default'

2. Combining with Ternary Operator:

let a = null;
let b = undefined;
let c = 'hello';

let result = a ?? b !== undefined ? b : c;

console.log(result); // Output: 'hello'

In this example, result is assigned the value of a if it is not null or undefined. If a is null or undefined, then the ternary operator checks if b is defined. If b is defined, then result is assigned its value. Otherwise, result is assigned the value of c.

3. chaining double question marks:

const data = {
  name: 'John',
  age: 0,

const result = data.name ?? data.age ?? 'Guest';

console.log(result); // Output: 'John'

This is a classic chaining example. in case the data.name is null or undefined, the data.age will be checked and if it’s also NULL or undefined, the function will return the default value of ‘Guest’.

These demonstrate the versatility and power of double question marks in JavaScript. Whether you are using it for error handling or combining it with other operators, it can make your code more concise and efficient. Incorporating double question marks into your JavaScript toolkit will make you a more effective and efficient developer.


In , the introduction of the double question marks in JavaScript is a welcome addition to the language. It allows for cleaner and more concise code, making it easier to read and maintain. Its ability to check for undefined or null values is especially useful in preventing bugs and errors.

As with any new feature, it is important to use it appropriately and with an understanding of how it works. While it may be tempting to rely solely on the double question marks for null checking, it is still important to consider other edge cases and potential sources of errors.

In any case, it is clear that the double question marks have become a valuable tool in the JavaScript developer's arsenal. Its simplicity and effectiveness have quickly won over the community, and it is sure to play an even bigger role in the language's future.

Cloud Computing and DevOps Engineering have always been my driving passions, energizing me with enthusiasm and a desire to stay at the forefront of technological innovation. I take great pleasure in innovating and devising workarounds for complex problems. Drawing on over 8 years of professional experience in the IT industry, with a focus on Cloud Computing and DevOps Engineering, I have a track record of success in designing and implementing complex infrastructure projects from diverse perspectives, and devising strategies that have significantly increased revenue. I am currently seeking a challenging position where I can leverage my competencies in a professional manner that maximizes productivity and exceeds expectations.
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