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 | Description |
|---|---|
false |
The keyword false. |
0 |
The Number zero (so, also 0.0, etc., and 0x0). |
-0 |
The Number negative zero (so, also -0.0, etc., and -0x0). |
0n |
The BigInt zero (so, also 0x0n). Note that there is no BigInt negative zero — the negation of 0n is 0n. |
"", '', `` |
Empty string value. |
| null | null — the absence of any value. |
| undefined | undefined — the primitive value. |
| NaN | NaN — not a number. |
document.all |
Objects are falsy if and only if they have the [[IsHTMLDDA]] internal slot.That slot only exists in document.all and cannot be set using JavaScript. |
Examples
Examples of falsy values in JavaScript (which are coerced to false in Boolean contexts, and thus bypass the if block):
if (false)
if (null)
if (undefined)
if (0)
if (-0)
if (0n)
if (NaN)
if ("")
The logical AND operator, &&
If the first object is falsy, it returns that object
false && "dog"
// ↪ false
0 && "dog"
// ↪ 0