Javascript conditional statement with a single pipe “|”

Question

Just wondering if anyone has come across this before.

I found in a project (that was handed over from another developer) a conditional statement that looked somethin

Answer 1

This is a bitwise OR operator. It will first convert it into a 32 bit integer, then apply the bitwise OR operation to the two numbers that result. In this instance, since Boolean(1) is true and Number(true) is 1, it will work fine without issue (the == operator will always return a boolean, and a if statement converts anything to a boolean). Here are a few examples of how it works:

1 | 0; // 1
0 | 0; // 0
0 | 1; // 1
1 | 1; // 1
true | false; // 1
false | false; // 0
2 | 1; // 3 (00000010, 00000001) -> (00000011)

As both sides have to be converted to a number (and therefore evaluated), this may cause unexpected results when using numbers when the logical OR statement (||) was meant to be used. For this, take these examples:

var a = 1;
a | (a = 0);
console.log(a); // 0

var b = 1;
b || (b = 0);
console.log(b); // 1

// I wanted the first one
var c = 3 | 4; // oops, 7!

Reference: http://www.ecma-international.org/ecma-262/5.1/#sec-11.10