Falsy
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):
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:
console.
log
(
false
&&
"dog"
)
;
// ↪ false
console.
log
(
0
&&
"dog"
)
;
// ↪ 0