## Pure Vanilla Javascript download and upload functions for Apache Cordova

The cordova plugin `cordova-plugin-file-transfer` is [due to be deprecated](https://cordova.apache.org/blog/2017/10/18/from-filetransfer-to-xhr2.html) and its latest [npm version fails on iOS](https://github.com/apache/cordova-plugin-file-transfer/issues/297).

Therefore these two working functions are purely based on JS, and thus no need to use extra plugins, besides the standard plugin `cordova-plugin-file`. Therefore this is compatible with any platform.

```js
// for different types of cordovaFileSystem check here: 
// https://cordova.apache.org/docs/en/latest/reference/cordova-plugin-file/#where-to-store-files
// or simply type in the console `console.log(cordova.file)`
function downloadFileToDevice (fileurl, filename, cordovaFileSystem, callback) {
  var onerror = (err) => {
    console.error(`Error downloading from ${fileurl} to cordovaFileSystem ${cordovaFileSystem}`, 
    err, new Error(err))
    if (typeof callback === 'function') { callback(Error(err)) }
  }

  var blob = null
  var xhr = new XMLHttpRequest()
  xhr.open('GET', fileurl)
  xhr.responseType = 'blob' // force the HTTP response, response-type header to be blob
  xhr.onload = () => {
    blob = xhr.response // xhr.response is now a blob object
    var DataBlob = blob
    window.resolveLocalFileSystemURL(cordovaFileSystem, (dirEntry) => {
      const sanitizedFilename = filename.replace(/[^a-z0-9\.]/gi, '_').toLowerCase() // sanitize filename
      dirEntry.getFile(sanitizedFilename, { create: true }, (file) => {
        file.createWriter((fileWriter) => {
          fileWriter.write(DataBlob)
          if (typeof callback === 'function') { callback(null, cordovaFileSystem + sanitizedFilename) }
        }, (err) => { console.error('Error on file.createWriter'); onerror(err) })
      }, (err) => { console.error('Error on dirEntry.getFile'); onerror(err) })
    }, (err) => { console.error('Error on resolveLocalFileSystemURL'); onerror(err) })
  }
  xhr.onerror = (err) => { console.error('Error on XMLHttpRequest'); onerror(err) }
  xhr.send()
}
```

```js
function uploadFileToServer (fileUri, fileName, remoteUrl, callback) {
  var onerror = (err) => {
    console.error(`Error uploading file ${fileUri} to ${remoteUrl}`,
      err, new Error(err))
    if (typeof callback === 'function') { callback(Error(err)) }
  }

  window.resolveLocalFileSystemURL(fileUri, function (fileEntry) {
    fileEntry.file((file) => {
      if (!file.size) { onerror('File is empty (on fileEntry from resolveLocalFileSystemURL)'); return }
      var reader = new FileReader()
      reader.onloadend = () => {
        var blob = new Blob([new Uint8Array(reader.result)], { type: 'application/octet-stream' })
        if (!blob.size) { onerror('File is empty (on blob)'); return }
        var fd = new FormData()
        fd.append('file', blob, fileName)

        var xhr = new XMLHttpRequest()
        xhr.open('POST', remoteUrl, true)
        xhr.onload = function () {
          if (xhr.status === 200 || xhr.status === 201) {
            if (typeof callback === 'function') { callback() }
          } else {
            console.error('Error on xhr.status: ' + xhr.status); onerror(xhr.status)
          }
        }
        xhr.onerror = (err) => { console.error('Error on XMLHttpRequest'); onerror(err) }
        xhr.send(fd)
      }
      reader.onerror = (err) => { console.error('Error on FileReader'); onerror(err) }
      reader.readAsArrayBuffer(file)
    }, (err) => { console.error('Error on fileEntry.file'); onerror(err) })
  }, (err) => { console.error('Error on resolveLocalFileSystemURL'); onerror(err) })
}
```

An example for download

```js
downloadFileToDevice('https://example.com/img.jpg',
  'myImg.jpg', 
  cordova.file.cacheDirectory,
  (err, localFilePath) => {
    if (err) {
      console.error('An error occured downloading file:', err)
    } else {
      console.log('Download file with success: ' + localFilePath)
    }
})
```

An example for upload, exactly as the `ft.upload` in `cordova-plugin-file-transfer`

```js
uploadFileToServer('file:///storage/emulated/0/Android/data/myfile.jpg',
  'myfileNameOnServer.jpg',
  'https://example.com/upload_url',
  (err) => {
    if (err) {
      console.error('Error uploading file:', err)
    } else {
      console.log('Upload done it with success')
    }
  })
  ```