What does two question marks mean in JavaScript? This is a question that often arises among developers who are new to the language or those who are trying to understand its more advanced features. In JavaScript, double question marks, known as the nullish coalescing operator, play a crucial role in simplifying code and improving readability. Let’s delve into this operator and explore its significance in the JavaScript ecosystem.
The nullish coalescing operator, represented by `??`, was introduced in ECMAScript 2020 (also known as ES11). It is designed to provide a more intuitive way of handling null and undefined values when assigning default values. Before the introduction of this operator, developers had to rely on the logical OR operator (`||`) to achieve similar functionality, which could sometimes lead to unexpected results.
To understand the purpose of the nullish coalescing operator, let’s consider a scenario where we want to assign a default value to a variable that might be null or undefined. Suppose we have a function that returns a user’s name, and there’s a possibility that the user might not have a name assigned yet. In such cases, we would use the logical OR operator to provide a default value:
“`javascript
const userName = getUser() || ‘Guest’;
“`
In the above code, if `getUser()` returns null or undefined, the variable `userName` will be assigned the value `’Guest’`. However, this approach has a limitation. If `getUser()` returns an empty string or an empty array, the variable `userName` will still be assigned the value `’Guest’`, which might not be the desired behavior.
This is where the nullish coalescing operator comes into play. It only considers null and undefined as “falsy” values and provides a more precise way of assigning default values:
“`javascript
const userName = getUser() ?? ‘Guest’;
“`
In this code, if `getUser()` returns null, undefined, or an empty string, the variable `userName` will be assigned the value `’Guest’`. However, if `getUser()` returns an empty array or any other falsy value other than null or undefined, the variable `userName` will retain the value returned by `getUser()`.
The nullish coalescing operator is not only useful for assigning default values but also for simplifying code that involves nested ternary operators. For example, consider the following code snippet:
“`javascript
const age = person?.age ?? 18;
“`
In this code, the nullish coalescing operator is used in conjunction with the optional chaining operator (`?.`). If `person` is null or undefined, or if `person.age` is null or undefined, the variable `age` will be assigned the value `18`. Otherwise, it will retain the value of `person.age`.
In conclusion, the double question marks in JavaScript, known as the nullish coalescing operator, provide a more intuitive and precise way of handling null and undefined values. By using this operator, developers can simplify their code, improve readability, and avoid unexpected results. As JavaScript continues to evolve, the nullish coalescing operator is expected to become an essential part of the language’s syntax.
