I know that null
is an object with no attributes or functions.
However, I am confused that why console.log(null == false);
and console.log(null == true);
both return false.
What are the conversion rules between null
and boolean
?
I know that null
is an object with no attributes or functions.
However, I am confused that why console.log(null == false);
and console.log(null == true);
both return false.
What are the conversion rules between null
and boolean
?
This is because the Abstract Equality Comparison Algorithm requires that if Type(x)
or Type(y)
is a Boolean in the expression x == y
then the Boolean value should be coerced to a number via ToNumber
, which converts true
to 1 and false
to +0
.
This means that any comparison of true == something
or something == true
results in 1 == something
or something == 1
(replacing true
and 1
with false
and +0
for false
).
The Null type does not compare as equal to either 1 or +0 (in fact, null is only comparable to undefined
in the Abstract Equality Comparison Algorithm).
There is a detailed discussion of all of the different kinds of equality in JavaScript on MDN that is well worth looking at if you want to know more.
However, if you coerce null
to a number it is coerced to +0
so +null == false
actually returns true
.