# What does the “|” (single pipe) do in JavaScript?

``````console.log(0.5 | 0); // 0
console.log(-1 | 0);  // -1
console.log(1 | 0);   // 1
``````

Why does `0.5 | 0` return zero, but any integer (including negative) returns the input integer? What does the single pipe ("|") do?

This is a bitwise or.
Since bitwise operations only make sense on integers, `0.5` is truncated.

`0 | x` is `x`, for any `x`.

Bit comparison is so simple it's almost incomprehensible ;) Check out this "nybble"

``````   8 4 2 1
-------
0 1 1 0 = 6  (4 + 2)
1 0 1 0 = 10 (8 + 2)
=======
1 1 1 0 = 14 (8 + 4 + 2)
``````

Bitwise ORing 6 and 10 will give you 14:

``````   alert(6 | 10); // should show 14
``````

Terribly confusing!

A single pipe is a bit-wise OR.

Performs the OR operation on each pair of bits. a OR b yields 1 if either a or b is 1.

JavaScript truncates any non-integer numbers in bitwise operations, so its computed as `0|0`, which is 0.

``````
var testPipe = function(input) {
console.log('input => ' + input);
console.log('single pipe | => ' + (input | 'fallback'));
console.log('double pipe || => ' + (input || 'fallback'));
console.log('-------------------------');
};

testPipe();
testPipe('something');
testPipe(50);
testPipe(0);
testPipe(-1);
testPipe(true);
testPipe(false);``````