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

async function should have await expression JS-0116

Bug risk

Minor

a year ago — 2 years old

Found async function without any await expressions

118        return receiver
119    }
120
121    router.post("/api/post",  async (req, res) => {122        try {123          let message   = validateMessage(req.body.message);124          validatePID(req.body.pid);125          let reply_id  = validateReplyID(req.body.reply_id);126          let receiver  = validateReceiver(req.body.receiver);127128          let __dirname = server.dirname129          const file_names = ["","","","",""]130          if(isNotNull(req.files)) {131            for(let file_index=0;file_index<5;file_index++) {132              if(isNotNull(req.files[`file_${file_index}`])) {133                let file = req.files[`file_${file_index}`]134                const file_id = server.genstring(20)135                const file_name = `${file_id}/${(file.name.substring(0,25)).replace(/\.[^/.]+$/, "")}`136                let extension = file.name.substring(file.name.lastIndexOf("\.")+1)137                file_names[file_index]=`${file_name}${(extension in image_types && ".webp") || extension}`138                server.ensureExists(`${__dirname}/user_uploads/${file_id}`,undefined,async (err)=>{139                  if(err) {140                    console.error(err)141                    return;142                  }143                  if(extension in image_types) {144                    writeFile(`${__dirname}/user_uploads/${file_name}.webp`,await sharp(file.data).webp({mixed:true,effort:6}).toBuffer(),(err2)=>{145                      if(err2)console.error(err2)146                    })147                    server.ensureExists(`${__dirname}/user_uploads/previews/${file_id}`,undefined,async (error) => {148                      if(error) {149                        console.error(error)150                        return;151                      }152                      writeFile(`${__dirname}/user_uploads/previews/${file_name}.webp`,await sharp(file.data).resize(100,100,{fit: "inside"}).webp({mixed:true,effort:6}).toBuffer(),(error2)=>{153                        if(error2)console.error(error2)154                      })155                    })156                  } else {157                    file.mv(`${__dirname}/user_uploads/${file_name}.${extension}`,(err2)=>{158                       if(err2)console.error(err2)159                    })160                  }161                })162              }163            }164          }165166          let sql = `START TRANSACTION;INSERT INTO ipost.posts (post_user_name,post_text,post_time,post_receiver_name,post_from_bot,post_reply_id,file_0,file_1,file_2,file_3,file_4) VALUES (?,?,?,?,?,?,?,?,?,?,?);SELECT LAST_INSERT_ID() as ID;COMMIT;`;167          let values = [encodeURIComponent(res.locals.username), message, Date.now(), receiver, res.locals.isbot, reply_id,...file_names];168          con.query(sql, values, function (err, result) {169            if (err){170                res.status(500)171                res.json({"error":"there's been an interal error"})172                console.error(err)173                return;174            }175            let post_obj = {176                post_user_name: encodeURIComponent(res.locals.username),177                post_text: req.body.message,178                post_time: Date.now(),179                post_special_text: "",180                post_receiver_name: req.body.receiver,181                post_from_bot: res.locals.isbot,182                post_reply_id: reply_id,183                user_avatar: res.locals.avatar,184                files: file_names,185                post_id: result[0].ID186            };187            let message = {188                message: "new_post",189                data: post_obj190            };191            let messagestr = JSON.stringify(message);192            //console.log(5,server.wss.clients);       /* DEBUG: Log websocket clients */193            server.wss.clients.forEach(function(ws) {194                //console.log(5,ws); /* DEBUG: Log websocket clients */195                ws.send(messagestr);196            });197            res.json({ "success": "successfully posted message" });198            console.log(5, `posted new message by ${res.locals.username} : ${req.body.message}`);199          });200        } catch (error) {201            if(error.statusCode) {202                res.status(error.statusCode)203                res.json({ "error": error.message, "status": error.statusCode });204            } else {205                console.error("some error: ", error)206                res.status(500)207                res.json({"error":"internal server error", "status": 500})208            }209        }210        /* #swagger.security = [{211            "appTokenAuthHeader": []212        }] */213    });214    return createPID
215};
216export default {

Found async function without any await expressions

js/dms.js

 11var currentChannel
 12
 13let socket = new WebSocket(wss_URI);
 14socket.addEventListener("message", async function (_event) { 15	console.info("TODO: add websocket support to dms") 16	// return 17  // if(wss_server === event.origin) { 18  //   let data = event.data; 19  //   let ds = JSON.parse(data) 20  //   let message = ds.message 21  //   let item = ds.data 22  //   let username = decodeURIComponent(item.post_user_name) 23  //   if(message === "new_post") { 24  //     await createPost(decodeURIComponent(item.post_user_name),decodeURIComponent(item.post_text),item.post_time,item.post_special_text,highest_id+1,item.post_from_bot,item.post_reply_id,true) 25  //     if(user["username"]!==username)mainNoti(username) 26 27  //     let highest_known_posts = await (await fetch(`/api/getPostsLowerThan?id=${highest_id+28}&channel=${currentChannel}`)).json() 28  //     for (let i = 0; i < highest_known_posts.length; i++) { 29  //       if(document.getElementById(highest_known_posts[i].post_id) === undefined) { 30  //         main() 31  //         return; 32  //       } 33  //     } 34  //     highest_id++; 35  //   } 36  // } 37}) 38
 39var cd = true //inversed "cooldown"
 40

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") });

002Hub / IPost

Bad Practice

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