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

async function should have await expression JS-0116

Bug risk

Minor

15 days ago — 2 years old

Found async function without any await expressions

58    res.send(ret);
59};
60
61const getDefaults = async (req: Request, res: Response, next: NextFunction) => {62    console.log(req.query, req.query.mint, req.query["mint"]);63    let primitive = req.query.mint;64    let key = primitive as string;65    let technology = ComponentAPI.getComponentWithMINT(key);6667    if (technology === null) {68        console.error("Could not find MINT:", key);69        return res.status(400).send({ message: `MINT Not found - ${key}` });70    }71    console.log("Defaults:", primitive, technology.defaults);72    return res.send(technology.defaults);73};74
75export default { getDimensions, getTerminals, getDefaults };

Found async function without any await expressions

src/server/controller.ts

27    return res.send({"x-span":ret.xspan, "y-span":ret.yspan});
28};
29
30const getTerminals = async (req: Request, res: Response, next: NextFunction) => {31    let primitive = req.query.mint;32    let key = primitive as string;33    let technology = ComponentAPI.getComponentWithMINT(key);3435    if (technology === null) {36        console.error("Could not find MINT:", key);37        return res.status(400).send({ message: `MINT Not found - ${key}` });38    }3940    let params_text = req.query.params as string;41    let params = JSON.parse(params_text);42    console.log("Params:", params);43    params["position"] = [0, 0];44    params["color"] = "#FFF";4546    // console.log("Dimensions:",xspan, yspan);47    let ports = technology.getPorts(params);48    const drawoffsets = technology.getDrawOffset(params);4950    let ret = [];51    for (let i = 0; i < ports.length; i++) {52        let port = ports[i];53        port.x = Math.floor(port.x + drawoffsets[0]);54        port.y = Math.floor(port.y + drawoffsets[1]);55        ret.push(port.toInterchangeV1());56    }57    console.log("Terminals:", primitive, ret);58    res.send(ret);59};60
61const getDefaults = async (req: Request, res: Response, next: NextFunction) => {
62    console.log(req.query, req.query.mint, req.query["mint"]);

Found async function without any await expressions

src/server/controller.ts

 5
 6paper.setup(new paper.Size([64000, 48000]));
 7
 8const getDimensions = async (req: Request, res: Response, next: NextFunction) => { 9    let primitive = req.query.mint;10    let key = primitive as string;11    let technology = ComponentAPI.getComponentWithMINT(key);1213    if (technology === null) {14        console.error("Could not find MINT:", key);15        return res.status(400).send({ message: `MINT Not found - ${key}` });16    }1718    let params_text = req.query.params as string;19    let params = JSON.parse(params_text);20    console.log("Params:", params);21    params["position"] = [0, 0];22    params["color"] = "#FFF";23    params["rotation"] = 0;2425    let ret = technology.getDimensions(params);26    console.log("Dimensions:", primitive, ret);27    return res.send({"x-span":ret.xspan, "y-span":ret.yspan});28};29
30const getTerminals = async (req: Request, res: Response, next: NextFunction) => {
31    let primitive = req.query.mint;

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") });

CIDARLAB / 3DuF

Bad Practice

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