Rule proposal: Forbid !foo === bar

[fisker]

I'm not sure what name it should be, this is a common mistake, espeically when doing quick debugging. Personally I've done this several times.

We have this syntax forbidden in Prettier codebase, with no-restricted-syntax rule, because I made a mistake once there.

Fail

if (!foo === bar);

if (!foo !== bar);

// Don't have to be in `if`
const isEqual = !foo === bar;

Pass

if (!(foo === bar));

// I guess we should allow this, it's type-casting
if (!!foo === bar);

[sindresorhus]

no-negation-in-equality-check ?

[sindresorhus]

This looks similar to https://eslint.org/docs/rules/no-unsafe-negation Maybe that rule could support this too?

[fisker]

That rule not checking this case, but I can make a proposal there.

[fisker]

Forgot to mention here, issue on ESLint codebase eslint/eslint#14802, and seems they are going accept.

[fregante]

no-mixed-operators can already do this, if configured correctly.

• https://github.com/xojs/eslint-config-xo/issues/73

[fisker]

Accepted as no-negation-in-equality-check.