Suggestion: add flag to notify when awaiting a non-promise

Search Terms

async promise force error

Suggestion

Add a tsconfig.json flag to display info/warning/error when awaiting non-PromiseLike code. This will catch developer errors.

Use Cases

Catch developer errors when writing async code.

Example

The following code is valid:

await Promise.all(urls.map(url => {
  fetch(url);
});
console.log('fetching complete');

The developer intends to do something once all the fetches complete, but since map is not returning any value, it ends up awaiting [undefined, undefined, ...], which means fetching complete is logged before the fetches complete. It would be nice if TS gave an info/warning/error in this case.

The correct code is:

await Promise.all(urls.map(url => {
  return fetch(url);
});
console.log('fetching complete');

This example is paired down to the bare minimum for simplicity, but IRL code is more complex.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

issue ではソースファイルもテストも特定されていないため、まず TypeScript における await 式の処理と tsconfig の診断の場所を特定します。PromiseLike ではないコードを await する場合に、設定可能な info、warning、または error を定義して実装し、提供された Promise.all の例をカバーできれば完了です。