0" mean in JavaScript
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value | 0 value | 0 means "convert value to an integer"
| is the bitwise OR operator.
To work it first converts the values on both sides to signed 32bit integers then it does a bitwise OR of the values. Since bitwise OR with 0 does nothing this has the effect of just converting to an integer.
It is different that Math.floor in that it converts toward zero
| Math.floor | Math.ceil | Math.trunc | | 0 |
----------+------------+-----------+------------+------+
2.5 | 2 | 3 | 2 | 2 |
----------+------------+-----------+------------+------+
1.5 | 1 | 2 | 1 | 1 |
----------+------------+-----------+------------+------+
0.5 | 0 | 1 | 0 | 0 |
----------+------------+-----------+------------+------+
-0.5 | -1 | 0 | 0 | 0 |
----------+------------+-----------+------------+------+
-1.5 | -2 | -1 | -1 | -1 |
----------+------------+-----------+------------+------+
-2.5 | -3 | -2 | -2 | -2 |
----------+------------+-----------+------------+------+
Infinity | Infinity | Infinity | Infinity | 0 |
----------+------------+-----------+------------+------+
NaN | NaN | NaN | NaN | 0 |
----------+------------+-----------+------------+------+
2**32+5 | 4294967301 |4294967301 | 4294967301 | 5 |
----------+------------+-----------+------------+------+
That last one, 2*32+5 is a value that does not fit in 32 bits to point out you need to know when | 0 | 0 is appropriate and when it's not.
| 0 | 0 is also significantly faster than Math.floor or Math.ceil . There may be many reasons it's faster the most obvious is it's an operator, not a function on the Math object which can be replaced and therefore has to be checked on each usage.
It has a very low precedence which means you can usually tack it on to the end of an expressions without parenthesis
integerResult = someValue / someOtherValue | 0;
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