最佳替代var x = y || 假

Question

A codebase I'm working on contains many uses of the javascript 'default operator' such as:

var x = y || false;

I'm wondering what the best possible replacement to use in order to guarantee that the value is never undefined, null, etc. Should I replace them with "false" and check against the string? Should I replace them with their longhand counterpart (explicit checks for null and undefined)? Or does each use case need to be evaluated for something I'm not taking into account?

Answer 1

To set a non-falsy default when your input could be a valid falsy value, one way is to do two tests

if (!x && x !== 0) {
    x = 1; // 1 is the default value but 0 is a valid input
}

The advantage of doing it like this is you can exclude non-valid falsy values, eg NaN

---

This said, you may be better off casting or type checking

if (typeof x !== 'number') x = 1;

or

x = +x;
if (x !== x) x = 1; // NaN goes to default