await is only valid in async function

Question

I wrote this code in lib helper js var myfunction   async function x y               return  variableA  variableB    exports myfunction   myfunction   and then I tried to use it in another file  var helper   require    helper js        var start   function a b                  const result   await helper myfunction  test   test        exports start   start   I got an error   quot await is only valid in async function quot   What is the issue

User · Answer

await is only valid in async function   But why   await  explicitly turns an async call into a synchronous call  and therefore the caller cannot be async  or asyncable  - at least  not because of the call being made at  await

User · Answer

I had the same problem and the following block of code was giving the same error message   repositories forEach  repo   gt            const commits   await getCommits repo           displayCommit commits         The problem is that the method getCommits   was async but I was passing it the argument repo which was also produced by a Promise  So  I had to add the word async to it like this  async repo  and it started working   repositories forEach  async repo    gt            const commits   await getCommits repo           displayCommit commits

User · Answer

If you are writing a Chrome Extension and you get this error for your code at root  you can fix it using the following  quot workaround quot   async function run            Your async code here     const beers   await fetch  quot https   api punkapi com v2 beers quot       run     Basically you have to wrap your async code in an async function and then call the function without awaiting it

User · Answer

To use await  its executing context needs to be async in nature  As it said  you need to define the nature of your executing context where you are willing to await a task before anything    Just put async before the fn declaration in which your async task will execute   var start   async function a  b          Your async task will execute with await   await foo     console log  I will execute after foo get either resolved rejected       Explanation    In your question  you are importing a method which is asynchronous in nature and will execute in parallel  But where you are trying to execute that async method is inside a  different execution context which you need to define async to use await    var helper   require    helper js        var start   async function a b                  const result   await helper myfunction  test   test        exports start   start    Wondering what s going under the hood  await consumes promise future   task-returning methods functions and async marks a method function as capable of using await    Also if you are familiar with promises  await is actually doing the same process of promise resolve  Creating a chain of promise and executes you next task in resolve callback   For more info you can refer to MDN DOCS

User · Answer

The error is not refering to myfunction but to start   async function start                 const result   await helper myfunction  test    test           x000D   x000D     My function x000D  const myfunction   async function x  y    x000D    return   x000D      x  x000D      y  x000D       x000D    x000D   x000D     Start function x000D  const start   async function a  b    x000D    const result   await myfunction  test    test    x000D     x000D    console log result   x000D    x000D   x000D     Call start x000D  start    x000D   x000D   x000D        I use the opportunity of this question to advise you about an known anti pattern using await which is   return await     WRONG   x000D   x000D  async function myfunction     x000D    console log  Inside of myfunction    x000D    x000D   x000D     Here we wait for the myfunction to finish x000D     and then returns a promise that ll be waited for aswell x000D     It s useless to wait the myfunction to finish before to return x000D     we can simply returns a promise that will be resolved later x000D   x000D     useless async here x000D  async function start     x000D       useless await here x000D    return await myfunction    x000D    x000D   x000D     Call start x000D   async     gt    x000D    console log  before start    x000D   x000D    await start    x000D     x000D    console log  after start    x000D        x000D   x000D   x000D      CORRECT   x000D   x000D  async function myfunction     x000D    console log  Inside of myfunction    x000D    x000D   x000D     Here we wait for the myfunction to finish x000D     and then returns a promise that ll be waited for aswell x000D     It s useless to wait the myfunction to finish before to return x000D     we can simply returns a promise that will be resolved later x000D   x000D     Also point that we don t use async keyword on the function because x000D     we can simply returns the promise returned by myfunction x000D  function start     x000D    return myfunction    x000D    x000D   x000D     Call start x000D   async     gt    x000D    console log  before start    x000D   x000D    await start    x000D     x000D    console log  after start    x000D        x000D   x000D   x000D      Also  know that there is a special case where return await is correct and important    using try catch   Are there performance concerns with  return await

User · Answer

When I got this error  it turned out I had a call to the map function inside my  async  function  so this error message was actually referring to the map function not being marked as  async    I got around this issue by taking the  await  call out of the map function and coming up with some other way of getting the expected behavior   var myfunction   async function x y                 someArray map someVariable   gt        lt - This was the function giving the error         return await someFunction someVariable

User · Answer

async await is the mechanism of handling promise  two ways we can do it  functionWhichReturnsPromise                then result   gt                    console log result                               cathc err   gt                    console log result                      or we can use await to wait for the promise to full-filed it first  which means either it is rejected or resolved    Now if we want to use await  waiting for a promise to fulfil  inside a function  it s mandatory that the container function must be an async function because we are waiting for a promise to fulfiled asynchronously    make sense right    async function getRecipesAw                const IDs   await getIds     returns promise             const recipe   await getRecipe IDs 2       returns promise             return recipe     returning a promise                    getRecipesAw   then result  gt               console log result              catch error  gt               console log error

User · Answer

The current implementation of async   await only supports the await keyword inside of async functions Change your start function signature so you can use await inside start     var start   async function a  b          For those interested  the proposal for top-level await is currently in Stage 2  https   github com tc39 proposal-top-level-await

User · Answer

Yes  await   async was a great concept  but the implementation is completely broken     For whatever reason  the await keyword has been implemented such that it can only be used within an async method   This is in fact a bug  though you will not see it referred to as such anywhere but right here   The fix for this bug would be to implement the await keyword such that it can only be used TO CALL an async function  regardless of whether the calling function is itself synchronous or asynchronous     Due to this bug  if you use await to call a real asynchronous function somewhere in your code  then ALL of your functions must be marked as async and ALL of your function calls must use await   This essentially means that you must add the overhead of promises to all of the functions in your entire application  most of which are not and never will be asynchronous   If you actually think about it  using await in a function should require the function containing the await keyword TO NOT BE ASYNC - this is because the await keyword is going to pause processing in the function where the await keyword is found   If processing in that function is paused  then it is definitely NOT asynchronous   So  to the developers of javascript and ECMAScript - please fix the await async implementation as follows      await can only be used to CALL async functions   await can appear in any kind of function  synchronous or asynchronous   Change the error message from  await is only valid in async function  to  await can only be used to call async functions

[javascript] await is only valid in async function

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