JavaScript Promise with FileReader

Question

I'm trying to return a split array when a user specifies a text file in an input box using promises, but the console.log keeps returning undefined, despite resolve actually finding the data.

I know im using the promise wrong but i just can't figure it out, any help would be very appreciated

class TextReader {
  readFile (event) {
    let file = event.target.files[0]
    var promise = Promise.resolve()
    pFileReader(file)
    promise.then(function (result) {
      console.log(result)
    })

    function pFileReader (file) {
      return new Promise((resolve, reject) => {
        var reader = new FileReader()
        reader.onload = function found () {
          resolve(reader.result)
        }
        reader.readAsText(file)
      })
    }
  }
}

This is the code in my html

<input type='file' accept='text/plain' id="file" onchange='ValidateInput(event)'/>

      function ValidateInput (event) {
        let myTextReader = new TextReader()
        let output = myTextReader.readFile(event)
      }

Shubham Khatri · Accepted Answer · 2018-09-25 07:27:04Z

4

A promise is returned by pFileReader and you need to resolve the returned Promise and not a new Promise

class TextReader {
  readFile (event) {
    let file = event.target.files[0]
    var promise = pFileReader(file)
    promise.then(function (result) {
      console.log(result)
    })

    function pFileReader (file) {
      return new Promise((resolve, reject) => {
        var reader = new FileReader()
        reader.onload = function found () {
          resolve(reader.result)
        }
        reader.readAsText(file)
      })
    }
  }
}

answered Sep 25, 2018 at 7:27

Shubham Khatri

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