Question

What’s the difference between | and || in Javascript?

Furthermore, what’s the difference between & and &&?

Answer 1

| is a bitwise or, || is a logical or.

A bitwise or takes the two numbers and compares them on a bit-by-bit basis, producing a new integer which combines the 1 bits from both inputs. So 0101 | 1010 would produce 1111.

A logical or || checks for the “truthiness” of a value (depends on the type, for integers 0 is false and non-zero is true). It evaluates the statement left to right, and returns the first value which is truthy. So 0101 || 1010 would return 0101 which is truthy, therefore the whole statement is said to be true.

The same type of logic applies for & vs &&. 0101 & 1010 = 0000. However 0101 && 1010 evaluates to 1010 (&& returns the last truthy value so long as both operands are truthy).