Deep Loader

Deep Loader is a class that helps keeping track of loading progress at several levels. For each loading task may consist of several other tasks, and perhaps there is a hierarchy of components that all need their children to finish their loading tasks before they are considered finished themselves.

Usage

Single loading task

let loader = new Loader();
loader.isLoading(); // false
loader.isFinished(); // false

loader.start();

loader.isLoading(); // true
loader.isFinished(); // false

loader.done();

loader.isLoading(); // false
loader.isFinished(); // true

Multiple loading tasks

Loaders can start multiple named tasks. Only if all of them are finished, the loader will be considered finished itself.

let loader = new Loader();
loader.isLoading(); // false
loader.isFinished(); // false

loader.start('task1');
loader.start('task2');

loader.isLoading(); // true
loader.isFinished(); // false

loader.finish('task1');

loader.isLoading('task1'); // false
loader.isFinished('task1'); // true

loader.finish('task2');

loader.isLoading(); // false
loader.isFinished(); // true

Nested loaders

Loaders can be nested, so that the parent needs to wait for the subloader to finish loading all its tasksbefore it can finish its own loading.

let loader = new Loader();
let subloader = new Loader();

loader.addSubLoader(subloader, 'sub');
subloader.start();

loader.isLoading(); // true

subloader.finish();

loader.isFinished(); // true

Existing Promises

Loaders can use exisitng promises as tasks and wait for those to finish as part of their own loading.

let loader = new Loader();
let pending = myAsynchronousFunction();
const promise = loader.start('task1', 5000, pending); // timeout of 5000 after which task is considered a failure
await promise; // will return a promise for the task, which will also include the timeout

Waiting for a task

A Loader can provide a Promise to wait for a specific task that may or may not have been started.

let loader = new Loader();
loader.wait('task1').then(()=>console.log("Finished task 1"));
loader.start('task1');
loader.finish('task1'); // will now resolve the wait

Payloads and events

Loading tasks can provide output:

let loader = new Loader();

loader.on(FinishEvent, value => console.log(value)); // "Result!"

loader.start('task1');
loader.finish('task1', "Result!");

Errors

If any of its tasks fail, the loader itself will not finish loading. Errors can be retrieved from the loader.

let loader = new Loader();
loader.start("task1");
loader.start("task2");

loader.on(ErrorEvent, error => console.error(error.message)); // "Loading failed"

loader.error("task1", new Error("Loading failed"));
loader.finish("task2");

console.log(loader.errors); // {task1: Error("Loading failed")}