CODEWITHSUNDEEP
javascriptasync-await
JorahFriendzone
JorahFriendzone

Reputation: 433

Promise not returning anything?

I've been trying to convert my promise syntax from then/catch to async/await and for some reason it's now unable to return my promise. This is the then/catch version which returns the data perfectly fine 

let lotFiles = []

export function returnData(key) {
  getContentWithKey(key)
  .then(content => {
    if (content.previousHash === '') {
      lotFiles.push(content)
      return lotFiles
    }
    lotFiles.push(content)
    returnData(content.previousHash)
  })
  .catch(err => {
    console.log(err);
  })
}

This is the async/await version which doesn't return anything at all

let lotFiles = []

async function returnData(key) {
  try {
    let content = await getContentWithKey(key)
    if (content.previousHash === '') {
      lotFiles.push(content)
      return lotFiles
    } else {
      lotFiles.push(content)
      returnData(content.previousHash)
    }
  } catch (e) {
      console.log(e);
    }
}

I have another function that calls returnData - 

async function returnContent(data) {
  let something = await getContent(data)
  console.log(something)
}

returnContent()

Upvotes: 0

Views: 94

Answers (1)

Dan Nagle
Dan Nagle

Reputation: 5425

async/await requires a promise chain.

The returnData() function is recursive so you can place the inner most result in an array and push the other results in the chain.

async function returnData(key) {
  try {
    const content = await getContentWithKey(key)
    if (content.previousHash === '') {
      // termination of recursion
      // resolve with an array containing the content
      return Promise.resolve([content])
    }
    else {
      return returnData(content.previousHash).then(function(result) {
        // append the result and pass the array back up the chain
        return [content].concat(result)
      })
    }
  }
  catch(error) {
    return Promise.reject(error)
  }
}

You can replace the inner promise chain with await.

async function returnData(key) {
  try {
    const content = await getContentWithKey(key)
    if (content.previousHash === '') {
      // termination of recursion
      // resolve with an array containing the content
      return Promise.resolve([content])
    }
    else {
      try {
        let result = await returnData(content.previousHash)
        // append the result and pass the new array back up the chain
        return [content].concat(result)
      }
      catch(error) {
        return Promise.reject(error)
      }
    }
  }
  catch(error) {
    return Promise.reject(error)
  }
}

Upvotes: 1

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