typescript Promise : 'await' expression is only allowed within an async function [duplicate]

Question

i have created below code to get some data, i am returning that data in a function and i am calling that function in a variable like below :

 let tmsValue = await GetTMS(fymcl,this.model); 
    console.log("tmsValue",tmsValue);

   let tms;
   var GetTMS = async function getTMS(yearMetricCombo, modelData) : Promise<any>{
     return new Promise((resolve, reject)=>{
     modelData
       .query("11111")
       .where("fymcl").equals(yearMetricCombo) // tm|FY18|Promtions
       .loadAll()
       .exec((error, data) => {
         if (error) {
           reject(error);
         } else {
           tms = String(data.Items[0].attrs.uploadtms);
           resolve(tms);
           // console.log("tms",tms); // iam getting value over here
         }
       });
       return tms;
     });
   }

The issue is let tmsValue = await GetTMS(fymcl,this.model); // this line is saying 'await' expression is only allowed within an async function.

I am not sure what i need to do.

Your function GetTMS has no return statement, so the function implicitly returns undefined. It looks like it's making an asynchronous db call, so you may want to look into using a Promise here. Take a look at this question — CRice
– CRice, Commented Apr 13, 2018 at 18:23
But now its saying await can only be used inside async function — user3205921
– user3205921, Commented Apr 13, 2018 at 19:55
Indeed, the await keyword can only be used in a function declared with the async keyword. That means it cannot appear at the root level of your file. If you need to use the getTMS function at the root of the file, you'll have to put the code that uses its result inside the .then callback of the promise. If you need to use getTMS in another function, you either need to use the .then method as mentioned, or mark the function as async. — CRice
– CRice, Commented Apr 13, 2018 at 20:01
i have marked it as async, can u please make some update in my code to include .then() — user3205921
– user3205921, Commented Apr 13, 2018 at 21:05

Ryan Cavanaugh · Accepted Answer · 2018-04-13 18:24:44Z

1

The function doesn't return:

 function GetTMS(yearMetricCombo, modelData){
      // NO RETURN STATEMENT HERE
      modelData
      .query("11111")
      .where("fymcl").equals(yearMetricCombo) // tm|FY18|Promtions
      .loadAll()
      .exec((error, data) => {
        console.log("error",error);
        if (error) {
        } else {
          let tms = String(data.Items[0].attrs.uploadtms);
          console.log("tms",tms);
          // this returns from the *arrow function*, not
          // the enclosing function declaration
          return tms;

        }
      });
      // NO RETURN STATEMENT HERE
    }

See the question linked to from @CRice's comment for how to return from an async call

answered Apr 13, 2018 at 18:24

Ryan Cavanaugh

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4 Comments

user3205921 Over a year ago

why i need a return statement at the top ?

Ryan Cavanaugh Over a year ago

You don't, I'm just listing the two places where a return statement could be but isn't

jfriend00 Over a year ago

This doesn't have anything to do with the OP's error they asked about. The OP's error is because they're trying to use await outside of an async defined function which you cannot do. That's a core requirement of using await.

Ryan Cavanaugh Over a year ago

OP has been substantially edited since I posted this :\

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