What does the "|" (single pipe) do in JavaScript?

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

x | 0 is x, if x is an integer.

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!

This example will help you.

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);

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.