Why is ( Infinity | 0 ) === 0?
I'm fiddling around with bitwise operators in JavaScript and there is one thing I find remarkable.
The bitwise or operator returns 1
as output bit if one of the two input bits are 1
.开发者_JS百科 So doing x | 0
always returns x
, because | 0
has no effect:
( 1 | 0 ) === 1
( 0 | 0 ) === 0
However, when I calculated Infinity | 0
, I got 0
. This is surprising in my opinion, because by the above one should get Infinity
. After all, ( x | 0 ) === x
.
I cannot find where in the ECMAscript specification this is explicitly defined, so I was wondering what exactly implies that ( Infinity | 0 ) === 0
. Is is perhaps the way Infinity
is stored in memory? If so, how can it still be that doing a | 0
operation causes it to return 0
whereas | 0
should not do anything?
Bitwise operators work on integers only.
Infinity
is a floating-point value, not an integer.
The spec says that all operands of bitwise operations are converted to integers (using the ToInt32 operation) before performing the operation.
The ToInt32 operation says:
If number is NaN, +0, −0, +∞ or –∞ return +0.
Doing math and other operations that expect integers with NaN
and Infinity
is usually a bad idea. How would you set/clear a bit from Infinity?
Actually, bit-wise operations are only defined for integers - and integers do not have NaN
or Infinity
.
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