The nullish coalescing operator ?? is a logical operator that returns the right-hand operand when the left-hand operand is null or undefined. It's useful when providing default values without incorrectly handling falsy values like 0, "", or false.

Use ?? to assign default values when a variable is null or undefined.

|| returns the right-hand operand if the left is any falsy value (like 0, "", false), while ?? only checks for null or undefined.

Chain ?? to provide fallback values in sequence.

Mixing ?? with || or && without parentheses causes a syntax error. Always use parentheses when mixing.