Question 202780 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Uncaught TypeError: (intermediate value).then is not a function

I can’t understand why I am getting the error in the subject:

var a = async function(){
    await setTimeout(function(){console.log('Hi');},2000);
    return(7);
  }.then((res)=>{console.log(res);});
  
  console.log(a());

It’s just a test to learn to work with async/await and promises, my code shouldn’t do anything meaningful

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2

Answers


  1. 0

    You should call .then on a Promise to get the result after it completes. Currently, you are attempting to call .then on a function, which does not have this method. You would need to call the async function to get a Promise, which you can then wait for.

    For example:

    (async function() {
  return 7;
})()/* note these parentheses */.then(console.log);

    Note that await does not make sense with setTimeout, as it does not return a Promise.

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  2. 0

    You can use this as a sample for trying out async/await with Promises

    const a = async function(){
    const samplePromise = new Promise((resolve,reject)=>{
        setTimeout(()=>{
            console.log('Hi')
            resolve(true)
        },2000)
    });
    await samplePromise;
}

a().then(()=>{
    console.log('a function is implemented')
})

    Few points to note:

    • You can await only Promises, setTimeout does not create Promises rather it is used to imitate a time taking process.
    • An async function always return Promises.
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