New rule proposal: disallow === -0

Please describe what the rule should do:

The rule should warn against code that tries to use the === operator to compare against -0, since that will not work as intended. That is, code like x === -0 will pass for both +0 and -0. The author probably intended Object.is(x, -0).

What category of rule is this? (place an “X” next to just one item)

[ ] Enforces code style [x] Warns about a potential error [ ] Suggests an alternate way of doing something [ ] Other (please specify:)

Provide 2-3 code examples that this rule will warn about:

// Don't accept negative zero
if (x === -0) {
  throw new TypeError("-0 is not a valid value for this API");
}

// This code intends to only throw on -0, but instead throws on +0 as well.

// Allow any negative number, including negative zero
if (x === -0 || x < 0) {
  // use x
}

// This code intends to disallow +0, but instead allows it through.

Why should this rule be included in ESLint (instead of a plugin)?

This rule seems like a fairly universal potential mistake. It meets all the core rule guidelines and is a perfect candidate for linting.

[domenic]

Sounds great, thanks! I’ll most likely work on this over the upcoming weekend.

[nzakas]

I can see an argument for this as a core rule, as it’s one of those language quirks that you could spend days trying to debug if you misunderstood what happens, and I agree with the comparison to use-isnan, as that rule solves a similar problem.

I’d even go so far as to say I think it should be included in “eslint:recommended”.

I’ll champion.

@domenic are you willing to submit a PR for this rule if the team accepts it?