ESLint + TypeScript + 更严格的 if 语句

Question

I've currently discovered a very subtle bug in my TypeScript project:

const makeDecision = (): Promise<boolean> => {
  return Promise.resolve(false);
};

const shouldDoIt = makeDecision(); // Oops! I forgot the await

if (shouldDoIt) {
  // do stuff
}

(I hand typed that just now, so there may be a mistake...)

In this particular example, I forgot the await keyword which caused shouldDoIt to be a Promise , rather than a boolean . So, it'll always be truthy in a if -statement. Because this is valid behavior for JavaScript, the TypeScript compiler doesn't complain a bit even though this was not my intention. Obviously, computers don't magically know my intention, but compilers can be very strict if need-be.

Is there a way to either configure ESLint or the TypeScript compiler to be more strict about if-statements to only allow boolean , rather than truthy types? Ideally, I'd love the compiler or ESLint to fail for statements like:

if ("a string") {
}

if (null) {
}

if (someNumber) {
}

Answer 1

The typescript-eslint rule strict-boolean-expressions does what you're looking for. Additionally, the no-unnecessary-condition rule would have caught your case too.