Application Life Cycle Hooks

Because feature-u is in control of launching the app, application life cycle hooks can be introduced, allowing features to perform app-specific initialization, and even inject components into the root of the app.

Two hooks are provided through the following built-in Feature aspects:

  1. Feature.appWillStart - invoked one time at app startup time
  2. Feature.appDidStart - invoked one time immediately after app has started


The Feature appWillStart() life-cycle hook is invoked one time, just before the app starts up.

API: appWillStart({app, curRootAppElm}): rootAppElm || falsy

This life-cycle hook can do any type of initialization. For example: initialize FireBase (say from a named DB feature's public API):

appWillStart({app, curRootAppElm}) {

In addition, this life-cycle hook can optionally supplement the app's top-level root element (i.e. react component instance). Any significant return (truthy) is interpreted as the app's new rootAppElm. IMPORTANT: When this is used, the supplied curRootAppElm MUST be included as part of this definition (accommodating the accumulative process of other feature injections)!

Here is an example that injects new root-level content:

appWillStart({app, curRootAppElm}) {
  ... any other initialization ...
  return (
    <Drawer ...>

Here is an example of injecting a new sibling to curRootAppElm:

appWillStart: ({app, curRootAppElm}) => [React.Children.toArray(curRootAppElm), <Notify key="Notify"/>]


The Feature appDidStart() life-cycle hook is invoked one time immediately after app has started.

API: appDidStart({app, [appState], [dispatch]}): void

Because the app is up-and-running at this time, you have access to the appState and dispatch() function ... assuming you are using redux (when detected by feature-u's plugable aspects).

A typical usage for this hook is to dispatch some type of bootstrap action. Here is a startup feature, that issues a bootstrap action:

appDidStart({app, appState, dispatch}) {
  dispatch( actions.bootstrap() );

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