lodash implementation of return value === 0 ? value : 0

Question

Can anyone explain why this line is used in lodash library.

if (!value) {
    return value === 0 ? value : 0;
}

and why not just return 0;

Answer 1

There are two different values which are considered strictly equal to zero: +0 and -0:

+0 === +0;
+0 === -0;
-0 === +0;
-0 === -0;

However, these values don't behave completely identically:

1 / +0 === +Infinity
1 / -0 === -Infinity

and clearly +Infinity !== -Infinity.

Then the code does this:

1. If value is "falsy" (undefined, null, false, +0, -0, NaN, "")
   1. If value is +0 or -0, it returns value
   2. Otherwise, it returns +0