Events

Data Provider includes an event emitter that allows to be continually informed about what is happening and react in consequence.

Normally, using the events API directly should not be necessary, as Data Provider addons usually make this job for you and provide all needed reactivity, but there are some cases in which can be useful.

Adding listeners

There are four methods available for adding listeners to providers or selectors: on, once, onChild and onceChild.

Their APIS are described in the providers and selectors methods API page, and their names should be descriptive enough to fully understand the purpose of each one, but, anyway:

• Methods prefixed with once automatically unsubscribe the provided listener after its first execution.
• Methods suffixed with Child subscribe the listener to events happening on any children (queried instances) of the provider or selector.

Arguments

As all mentioned methods require same arguments to be executed, we will use the on method as example in the API description:

on(eventName, listener)

Arguments

• eventName (String): Event name to subscribe to. Read events names chapter in this page for further info.
• listener (Function): The callback to be invoked when the specific eventName is dispatched.

Event names

In this chapter are described the eventNames common to all providers. Addons can emit its own eventNames, which should be described in its own documentation.

eventName

Available event names are:

• readStart: Dispatched when the read method has not cache and internally calls to the addon readMethod. When the provider or selector result is cached, this event is not dispatched.
• readSuccess: Dispatched when the read method is resolved successfully. When the provider or selector result is cached, this event is not dispatched.
• readError: Dispatched when the read method is rejected with an error.
• cleanCache: Dispatched when the provider cache is cleaned. Usually when the cleanCache method is executed, but not every times necessarily, as the provider can have configured the cleanCacheThrottle option, and this event will be dispatched only when the cache is cleaned really.
• init: Dispatched when a new provider or selector instance is created.
• resetState: Dispatched when the resetState method is executed.

eventName wildcard

You can also use next wildcard to listen to any of the events described before:

• *: Dispatched when any of the previously described event names are dispatched.

When using wildcards, the original eventName will be received as first argument in the listener function.

eventNames

All described event names are exported as constants in order to facilitate their usage. They are available at the eventNames property at top-level export of the library. The map of equivalences is:

• eventNames.READ_START: readStart
• eventNames.READ_SUCCESS: readSuccess
• eventNames.READ_ERROR: readError
• eventNames.CLEAN_CACHE: cleanCache
• eventNames.INIT: init
• eventNames.RESET_STATE: resetState
• eventNames.ANY: *

listener API

The provided listener function should follow the next API:

listener([eventName|child], [child])

Arguments

• eventName (String): When the listener was subscribed using the * wildcard, it will receive the eventName causing the execution as first argument.
• child (provider or selector) : When the listener was subscribed using a child method (onChild or onceChild) it will receive the child causing the execution as first argument, or in second argument in case the listener was subscribed using the * wildcard.

Examples

Basic example

import { eventNames } from "@data-provider/core";
import { books } from "data/books"; // books is a provider

books.on(eventNames.READ_START, eventName => {
  console.log("books has started read");
});

books.read();
// Books has started read

Using wildcard

import { eventNames } from "@data-provider/core";
import { books } from "data/books"; // books is a provider

books.on(eventNames.ANY, eventName => {
  console.log(`books ${eventName} event was dispatched`);
});

books.cleanCache();
// books cleanCache event was dispatched
books.read();
// books readStart event was dispatched

Child events

import { eventNames } from "@data-provider/core";
import { books } from "data/books"; // books is a provider

const authorBooks = books.query({ author: 2});

books.onChild(eventNames.CLEAN_CACHE, child => {
  console.log(`Cache of child of books with id ${child.id} was cleaned`);
});

books.onChild(eventNames.ANY, (eventName, child) => {
  console.log(`${eventName} was dispatched in child with id ${child.id}`);
});

await authorBooks.cleanCache();
// Cache of child of books with id books-{"author":2} was cleaned
// cleanCache was dispatched in child with id books-{"author":2}