What does the double question mark mean in JavaScript?

In JavaScript, the double question mark (??) is known as the Nullish Coalescing Operator. This operator provides a concise way to handle default values when dealing with null or undefined variables.

The Nullish Coalescing Operator works by evaluating the left-hand operand. If the left-hand operand is either null or undefined, the operator returns the right-hand operand. However, if the left-hand operand is anything other than null or undefined (e.g., 0, false, an empty string), it returns the left-hand operand.

Here's how it works in practice: For example, consider: const value = null ?? "default"; // value will be "default" And: const value2 = 0 ?? "default"; // value2 will be 0. Unlike the OR operator (||), which returns the right-hand operand for any "falsy" value, the Nullish Coalescing Operator is more precise, only intervening when a value is truly null or undefined.

This makes the Nullish Coalescing Operator particularly useful when you want to distinguish between missing values (null or undefined) and intentional "falsy" values. For example, if a user's setting is set to 0, using the || operator may treat this as an unset variable; however, the ?? will correctly recognize that the value exists.

Introduced in ES2020, the Nullish Coalescing Operator enhances JavaScript's ability to deal with default values, improving code readability and reducing potential bugs. It is now a widely used feature for setting fallback values within applications written in JavaScript.

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