Rule change proposal regarding `prefer-ternary`

Ternaries are a useful syntactic construct for const assignments. They reduce a let/if/else mess to (hopefully) a single line. They can also be misused in various ways. The current implementation of the rule always enforces the use of a ternary if both branches of an if/else expression return the same type. This is unfortunately coincidentally true for Promises and Errors. Take these two examples:

if (condition) {
  await doSomething();
} else {
  await doSomeOtherThing();
}

The rule corrects this to:

await (condition ? doSomething() : doSomeOtherThing());

if (condition) {
  throw new ThisKindOfError();
} else {
  throw new ThatKindOfError();
}

The rule corrects this to:

throw (condition ? new ThisKindOfError() : new ThatKindOfError());

Both cases I would categorize as misuse of ternaries, since they do nothing more than deduplicate a await/throw and make the code less readable.

However, I would still like the rule to catch valid cases, which mostly come in this form:

let someVariable;

if (condition) {
  someVariable = thisValue;
} else {
  someVariable = otherValue;
}

This is (correctly) corrected to:

const someVariable = condition ? thisValue : otherValue;

I propose that the rule should be configurable to only apply to assignments. This would exclude situations using await/throw/yield.

[yeldiRium]

Regarding

const promise = condition ? doSomething() : doSomeOtherThing();
await promise;

I agree that it is better than what the rule suggests, but it is still much worse than

if (condition) {
  await doSomething();
} else {
  await doSomeOtherThing();
}

since it conceals the potential side-effects of those asynchronous operations.

I am for the suggested more options, since in our case we prefer assignments and returns to be checked. If there are no other voices on this, a single option that only checks assignments and returns would be fine in my opinion. But I can see that others might only want assignments or even only returns.

[sindresorhus]

const promise = shouldUpdate ? updateDeployment(process.env.SMART_DEPLOYMENT_ID) : createDeployment(); await promise

Yeah, I agree. It seemed nice at first but having used it in practice, I agree, an if-statement would be better here.