Truthy vs. Falsy Values

Falsy values

JavaScript values are either truthy or falsy. All other values are truthy, such as non-empty strings, non-zero numbers, objects, arrays, and functions.

Empty arrays and objects are also truthy.

Logical operators

|| (OR)

Returns the first truthy value or the last value if all are falsy.

const value = "";
const safe = value || "fallback"; // "fallback"
 
const count = 0;
const safeCount = count || 10; // 10 — beware: 0 is falsy

&& (AND)

Returns the first falsy value or the last value if all are truthy.

const user = { name: "Alice" };
user && user.name; // "Alice"
 
null && "hidden"; // null

! (NOT)

Converts a value to its boolean opposite.

!true; // false
!""; // true
!!"hello"; // true (double negation for boolean coercion)

Nullish coalescing

??

Returns the right-hand value only if the left-hand value is null or undefined.

const value = "";
const safe = value ?? "fallback"; // "" — empty string is preserved
 
const count = 0;
const safeCount = count ?? 10; // 0 — zero is preserved