JS-0116 · `async function` should have `await` expression

async function should have await expression JS-0116

Bug risk

Minor

a year ago — a year old

Found async function without any await expressions

 52    });
 53}
 54
 55export async function asyncHttp<T = SuccessResponse>(request: Request) { 56  return fetch(request) 57    .then((r) => r.json()) 58    .then((data) => { 59      if (Object.prototype.hasOwnProperty.call(data, "dd")) { 60        window.dispatchEvent(new CustomEvent("__dd", { detail: data.dd })); 61      } else if (Object.prototype.hasOwnProperty.call(data, "whoops")) { 62        window.dispatchEvent( 63          new CustomEvent("__whoops", { detail: data.whoops }) 64        ); 65      } else if (Object.prototype.hasOwnProperty.call(data, "redirect")) { 66        document.location = data.redirect; 67      } 68      return data as T; 69    }); 70} 71
 72export function httpGet<T = SuccessResponse>(
 73  url: string,

Found async function without any await expressions

handvask_frontend/src/functions.ts

109  http<T>(r, callback);
110}
111
112export async function asyncHttpGet<T = SuccessResponse>(url: string) {113  const r = new Request(url, {114    method: "GET",115    headers: {116      "X-Requested-With": "XMLHttpRequest",117    },118  });119  return asyncHttp<T>(r);120}121
122export async function asyncHttpPost<T = SuccessResponse>(
123  url: string,

Found async function without any await expressions

handvask_frontend/src/functions.ts

119  return asyncHttp<T>(r);
120}
121
122export async function asyncHttpPost<T = SuccessResponse>(123  url: string,124  data: Record<string, unknown>125) {126  const r = new Request(url, {127    method: "POST",128    headers: {129      "Content-Type": "application/json",130      "X-Requested-With": "XMLHttpRequest",131    },132    body: JSON.stringify(data),133  });134  return asyncHttp<T>(r);135}

Description

A function that does not contain any await expressions should not be async (except for some edge cases in TypeScript which are discussed below). Asynchronous functions in JavaScript behave differently than other functions in two important ways:

The return value is always a Promise.
You can use the await operator inside them.

Functions are made async so that we can use the await operator inside them. Consider this example:

async function fetchData(processDataItem) {
    const response = await fetch(DATA_URL);
    const data = await response.json();

    return data.map(processDataItem);
}

Asynchronous functions that don't use await might be an unintentional result of refactoring.

Note: This issue ignores async generator functions. Generators yield rather than return a value and async generators might yield all the values of another async generator without ever actually needing to use await.

In TypeScript, one might feel the need to make a function async to comply with type signatures defined by an interface. Ideally, the code should be refactored to get rid of such restrictions, but sometimes that isn't feasible (For example, when we are implementing an interface defined in a 3rd party library like Next.js).

This situation can easily be circumvented by returning the value with a call to Promise.resolve:

interface HasAsyncFunc {
  getNum: () => Promise<number>
}

// Not recommended:
const o: HasAsyncFunc = {
  async getNum() { return 1 }
}

// Recommended:
const o: HasAsyncFunc = {
  // We only use `Promise.resolve` to adhere to the type
  // of the surrounding object.
  getNum() { return Promise.resolve(1) }
}

It is also advised to add a comment near the redundant promise to make the intent clear.

Bad Practice

async function fetchData(): string {
    // `readFileSync` is a synchronous function that blocks
    // the main thread, and thus does not need to be `await`ed
    return fs.readFileSync("data.txt", "utf-8");
}

performAction(async () => { console.log("no awaits in here") });

Handvask / handvask

Bad Practice

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