Question

I was just experimenting and tried putting this in the console:

4 | 2 | 4 | 1 | 10

returns 15 in console..

4 | 2 | 4 | 3 | 1

returns 7 in console..

I tried that on Chrome and Firefox.

Why?

I’m just starting with learning JavaScript… maybe I’m missing a concept here?

Answer 1

The | operator in JavaScript is a bitwise integer OR operator. So it’s doing an OR operation on the bits you’re giving it, resulting in 15.

A bitwise OR operation takes each bit in the value and sets the corresponding bit in the result if either of the input bits in that position is set. So

4  is 0100 in binary
2  is 0010
4  is 0100
1  is 0001
10 is 1010
      ----
      1111 = 15 decimal

Update: In a comment on your question, you’ve said you were expecting true rather than 15. If so, you want the logical OR operator, ||, not the bitwise operator, although || may also surprise you with what it returns (4 || 2 || 4 || 1 || 10 = 4, not true), as JavaScript’s logical OR (||) is curiously powerful, more so than in many other languages.