UploadTask interface

export interface UploadTask 

snapshot: UploadTaskSnapshot;

cancel(): boolean;

catch(onRejected: (error: StorageError) => unknown): Promise<unknown>;

on(event: TaskEvent, nextOrObserver?: StorageObserver<UploadTaskSnapshot> | null | ((snapshot: UploadTaskSnapshot) => unknown), error?: ((a: StorageError) => unknown) | null, complete?: Unsubscribe | null): Unsubscribe | Subscribe<UploadTaskSnapshot>;

var next = function(snapshot) {};
var error = function(error) {};
var complete = function() {};

// The first example.
uploadTask.on(
    firebase.storage.TaskEvent.STATE_CHANGED,
    next,
    error,
    complete);

// This is equivalent to the first example.
uploadTask.on(firebase.storage.TaskEvent.STATE_CHANGED, {
  'next': next,
  'error': error,
  'complete': complete
});

// This is equivalent to the first example.
var subscribe = uploadTask.on(firebase.storage.TaskEvent.STATE_CHANGED);
subscribe(next, error, complete);

// This is equivalent to the first example.
var subscribe = uploadTask.on(firebase.storage.TaskEvent.STATE_CHANGED);
subscribe({
  'next': next,
  'error': error,
  'complete': complete
});

// Just listening for completion, this is legal.
uploadTask.on(
    firebase.storage.TaskEvent.STATE_CHANGED,
    null,
    null,
    function() {
      console.log('upload complete!');
    });

// Just listening for progress/state changes, this is legal.
uploadTask.on(firebase.storage.TaskEvent.STATE_CHANGED, function(snapshot) {
  var percent = snapshot.bytesTransferred / snapshot.totalBytes * 100;
  console.log(percent + "% done");
});

// This is also legal.
uploadTask.on(firebase.storage.TaskEvent.STATE_CHANGED, {
  'complete': function() {
    console.log('upload complete!');
  }
});

var unsubscribe = uploadTask.on(
    firebase.storage.TaskEvent.STATE_CHANGED,
    function(snapshot) {
      var percent = snapshot.bytesTransferred / snapshot.totalBytes * 100;
      console.log(percent + "% done");
      // Stop after receiving one update.
      unsubscribe();
    });

// This code is equivalent to the above.
var handle = uploadTask.on(firebase.storage.TaskEvent.STATE_CHANGED);
unsubscribe = handle(function(snapshot) {
  var percent = snapshot.bytesTransferred / snapshot.totalBytes * 100;
  console.log(percent + "% done");
  // Stop after receiving one update.
  unsubscribe();
});

pause(): boolean;

resume(): boolean;

then(onFulfilled?: ((snapshot: UploadTaskSnapshot) => unknown) | null, onRejected?: ((error: StorageError) => unknown) | null): Promise<unknown>;