Falsy

A falsy (sometimes written falsey) value is a value that is considered false when encountered in a Boolean context.

JavaScript uses type conversion to coerce any value to a Boolean in contexts that require it, such as conditionals and loops.

The following table provides a complete list of JavaScript falsy values:

ValueTypeDescription
nullNullThe keyword null — the absence of any value.
undefinedUndefinedundefined — the primitive value.
falseBooleanThe keyword false.
NaNNumberNaN — not a number.
0NumberThe Number zero, also including 0.0, 0x0, etc.
-0NumberThe Number negative zero, also including -0.0, -0x0, etc.
0nBigIntThe BigInt zero, also including 0x0n, etc. Note that there is no BigInt negative zero — the negation of 0n is 0n.
""StringEmpty string value, also including '' and ``.
document.allObjectThe only falsy object in JavaScript is the built-in document.all.

The values null and undefined are also nullish.

Examples

Examples of falsy values in JavaScript (which are coerced to false in Boolean contexts, and thus bypass the if block):

js
if (false) {
  // Not reachable
}

if (null) {
  // Not reachable
}

if (undefined) {
  // Not reachable
}

if (0) {
  // Not reachable
}

if (-0) {
  // Not reachable
}

if (0n) {
  // Not reachable
}

if (NaN) {
  // Not reachable
}

if ("") {
  // Not reachable
}

The logical AND operator, &&

If the first object is falsy, it returns that object:

js
console.log(false && "dog");
// ↪ false

console.log(0 && "dog");
// ↪ 0

See also