A nullish value is a value that is either null or undefined in JavaScript. Nullish values are distinct from other falsy values (such as 0, '', and false) because they specifically represent the absence of a meaningful value rather than a value that evaluates to false in a boolean context.
- The nullish coalescing operator (
??) is commonly used in JavaScript to provide a default value for a variable that may be nullish. - Nullish values are often used to distinguish between a variable that has not been assigned a value and a variable that has been explicitly set to a nullish value.
Example:
let value1 = null;
let value2 = undefined;
let value3 = 0;
let value4 = '';
console.log(value1 ?? 'default'); // Output: 'default'
console.log(value2 ?? 'default'); // Output: 'default'
console.log(value3 ?? 'default'); // Output: 0 (0 is not nullish)
console.log(value4 ?? 'default'); // Output: '' (empty string is not nullish)