JavaScript Nullish Coalescing Operator

The Nullish Coalescing Operator (??) is a powerful feature in JavaScript that enables developers to manage null and undefined values with greater efficiency and clarity.

Key Concepts

• Purpose: The ?? operator provides a mechanism for establishing default values when working with variables that might be null or undefined.
• Behavior: It returns the right-hand operand when the left-hand operand is null or undefined. Otherwise, it returns the left-hand operand.

How It Works

In contrast to the logical OR operator (||), which returns the right-hand operand for any falsy value (such as 0, NaN, and ""), the nullish coalescing operator only considers null and undefined as triggers for returning the default value.

Syntax

let result = value1 ?? value2;

Here, result will be value1 if it is not null or undefined; otherwise, it will take the value of value2.

Examples

Comparison with Logical OR:

let count = 0;
let defaultCount = 10;

let finalCountUsingOr = count || defaultCount; // finalCountUsingOr is 10 (because 0 is falsy)
let finalCountUsingNullish = count ?? defaultCount; // finalCountUsingNullish is 0 (because 0 is not null or undefined)

Using with Defined Value:

let age = 25;
let defaultAge = 18;

let finalAge = age ?? defaultAge; // finalAge is 25

Basic Usage:

let name;
let defaultName = "Guest";

let finalName = name ?? defaultName; // finalName is "Guest"

Conclusion

The nullish coalescing operator is an invaluable tool in JavaScript for setting default values, particularly when aiming to avoid unintended behaviors caused by other falsy values. Its usage promotes clearer, more predictable code when handling potentially undefined or null values.