Truthy and Falsy Values

In JavaScript, a truthy value is a value that is considered true when encountered in a Boolean context. All values are truthy unless they are defined as falsy. That is, all values are truthy except false, 0, -0, 0n, "", null, undefined, and NaN.

JavaScript uses type coercion in Boolean contexts.

The following table provides a list of JavaScript falsy values:

Value	Description
false	The keyword false.
0, 0.0, 0x0	The Number zero.
-0, -0.0, -0x0	The Number negative zero.
0n, 0x0n	The BigInt zero.
"", '', ``	Empty string value.
null	null — the primitive value.
undefined	undefined — the primitive value.
NaN	NaN — not a number.

Examples of falsy values in JavaScript (which will be coerced to true in boolean contexts, and thus execute the if block):

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
}

Examples of falsy values in JavaScript (which will be coerced to true in boolean contexts, and thus execute the while block):

while (false) {
  // Not reachable
}
while (null) {
  // Not reachable
}
while (undefined) {
  // Not reachable
}
while (0) {
  // Not reachable
}
while (-0) {
  // Not reachable
}
while (0n) {
  // Not reachable
}
while (NaN) {
  // Not reachable
}
while ("") {
  // Not reachable
}