Tameable.js

Three functions for managing objects which depend on other objects to be in a valid state.

• We specify a key, and how to construct its object, with spec.
• We request to use objects by their keys with once.
• We invalidate an object by it's key with invalidate.

This ensure we minimise repeat work, only doing it when an object we need is not valid. Depending on how a dependancy tree is designed, work can be deffered in different ways. My specific usecase was with the WebGPU API in which pipelines and buffers have to be reconstructed when certain parameters change, such as screen size or rendering mode.

Tameable attempts to be small and low overhead.

Examples

Example 1 - Side-effects

import tame from 'tame'
tame.spec({key: 'shout once'}, async () => {
  console.log("Scream, and shout, and let it all out!");
  return tame.SUCCESS;
});

tame.once(['shout once']);
tame.once(['shout once']);
tame.once(['shout once']);

Note:

• Every spec function must return a non-null object (or a promise to one).
• We provide tame.SUCCESS if there is a situation where no objects need to be returned. ie we use the spec for it's side effects. It's a bit clearer than returning an empty object.

Example 2 - Render on demand

import tame from 'tameable'

// setup
tame.spec({key: 'renderObjects', deps: [...]}, async (...) => {
 // ...
 return renderObjects;
});
tame.spec(
 {
   key: 'render',
   deps: ['renderObjects']
 },
 async renderObjects => {
   // ..
   return tame.SUCCESS;
 }
);

// once(['renderObjects']);  // optionally preload, otherwise loaded on first frame

// render loop
async function frame() {
  await tame.once(['render'])  // only render if we need to
  requestAnimationFrame(frame);
}

// events
// render will be reconstructed on next call to `once`
event.on('something-happened', _ => invalidate('render')); 
// render and renderObjects will be reconstructed on next call to `once`
event.on('something-else-happened', _ => invalidate('renderObjects'));

Note:

• In this example, the 'render' spec function is called only once (unless an event is triggered) Hence, the once call only checks that the frame is up to date in most frames.
• If something does change the render is reconstructed, but only the dependancies which are invalid.
• If once was called without `await`` then any errors thrown will be uncaught and likley lead to console spam.

Example 3 - Wrapping callbacks

import tame from 'tame'
tame.spec({key: 'dom'}, async () => {
  if(document.readyState === 'loading') {
    // wrap 'DOMContentLoaded' callback with a promise
    return new Promise(resolve =>
      document.addEventListener('DOMContentLoaded', _ => resolve(document)));
  }
  return document;
});

// wait for dom to load
tame.once(['dom'])
  .then(_ => console.log('DOM loaded!'));

Note:

• This example shows a spec that waits for the DOM to be loaded. All dependants on dom will also wait.
• Circular dependencies are illegal.
• A spec function must return a non-null object, hence the use of document as a return value. If a promise is returned, it will be awaited and its return value will be the non-null object returned.

Mental model

• Each key is associated with an object which can be valid, validating, invalid, or initial.
• Each key has an associated function fn which returns a non-null javascript object.

When `spec`` is called,

• The list of dependencies, fn, and other info is stored under the key
• No work is done here

When once is called,

• For each key that is a dependency,
  • Lookup the key
  • If the object under the key is valid, return it
  • Otherwise, go to the first step for this object's dependencies
  • Then construct the object itself
  • If the constructed object is a non-null object, return it
  • Otherwise, throw an error

When invalidate is called,

• If the object under this key is valid
  • mark it as invalid
  • call invalidateFn if it exists
  • invalidate all objects that depend on this one
• Otherwise, do nothing
• No work is done here

About invalidate

• When an object is invalidated, so are all its children (dependants).
• Use invalidate in callbacks.
• If you find yourself using invalidate in a spec function but not a callback, maybe it should be in the dependancy list instead?
• Calling invalidate on an object that is validating or initial will do nothing, since these objects will be, or are being, reconstructed anyway.

Debug mode

Unless the library is bundled for production, extra checks will be performed and errors omitted for common mistakes such as forgetting to return a value from fn or creating a dependency on a key which doesn't yet exist (thus preventing circular dependencies). This features assumes a bundler and minifier will replace process.env.NODE_ENV !== 'production' with false and unreachable code will be optimised away, which it should. As such, errors in production code are less likley to be helpful. An error is only thrown in production if an objects fn returns a non-null object.

Future features to consider

• Tree analysis
• Tooling
• Promise.any / Promise.allSettled support, ie use whatever dependancy path first completes (usecases?)