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Falsy - Glossary | MDN
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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:
| Value | Type | Description |
|---|---|---|
| null | Null | The keyword null — the absence of any value. |
| undefined | Undefined | undefined — the primitive value. |
false |
Boolean | The keyword false. |
| NaN | Number | NaN — not a number. |
0 |
Number | The Number zero, also including 0.0, 0x0, etc. |
-0 |
Number | The Number negative zero, also including -0.0, -0x0, etc. |
0n |
BigInt | The BigInt zero, also including 0x0n, etc. Note that there is no BigInt negative zero — the negation of 0n is 0n. |
"" |
String | Empty string value, also including '' and ``. |
document.all |
Object | The 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
- Related glossary terms:
- Boolean coercion