The real-world app involves data loading via some API and showing UI based on the states of the API. For example, while data is loading, you may show a loader animation, but on error, you may show an error UI. This fairly simple-looking task ends up getting complex super fast and is more difficult to maintain with all the spaghetti code for UI synchronization. So here I propose the loadable pattern to simplify data loading and synchronize the UI with it.
In this example, we are going to load a list of todos. Here we are using react-redux as a state management solution. Below we will see how to create a store and reducer with react-redux. However, you can directly skip to "loadables" if you familiar with react-redux-context store.
Create react-redux context store
Let's start by creating a react-redux-context-store for storing our todos. The following sample is taken from react-redux.
// [filename: todo.store.jsx]
import React from 'react'
import {
Provider,
createStoreHook,
createDispatchHook,
createSelectorHook,
from "react-redux";
import { createStore } from "redux";
// reducer for the state
import { reducer } from "./store.reducer"
// react context store
const TodoContext = React.createContext(null)
// create redux state selector and dispatch from context
export const useTodoStore = createStoreHook(TodoContext)
export const useTodoDispatch = createDispatchHook(TodoContext)
export const useTodoSelector = createSelectorHook(TodoContext)
// create redux store from the reducer
const todoStore = createStore(reducer)
// create store provider wrap subtree
export function TodoStoreProvider({ children }) {
return (
<Provider context={TodoContext} store={todoStore}>
{children}
</Provider>
)
}
After creating a store provider we are going to create store.reducer.js
where we define the reducer and actions for the store.
// [filename: todo.reducer.js]
export const loadNext = () => ({ type: 'load_next' });
export const addTodos = ({ todos, total }) => ({ type: 'add_todos', payload: { todos, total } });
export const setLoading = (loading) => ({ type: 'set_loading', payload: { loading } });
const InitState = {
status: 'idle', // idle | pending | resolve | reject
todos: [],
total: 0,
skip: 0,
limit: 10
};
export const reducer = (state = InitState, action) => {
switch (action.type) {
case 'load_next': {
if (state.todos.length < state.total && state.status !== 'pending') {
return {
...state,
status: 'pending'
};
}
return state;
}
case 'add_todos': {
return {
...state,
status: 'resolve',
todos: [...state.todos, ...action.payload.todos],
total: state.total + action.payload.todos.length
};
}
case 'set_loading': {
return {
...state,
status: action.payload.loading
};
}
default: {
return state;
}
}
};
Loadable
Loadables are react components that wrap all data loading logic in it and update the store.
// [filename: App.js]
const App = () => (
<div>
<TodoStoreProvider>
{/* Loadable holds all data loading logic*/}
<TodoLoadable>
{/* Render todos */}
</TodoLoadable>
</TodoStoreProvider>
</div>
);
Now let's create a loadable:
// [filename: Todo.loadable.js]
function TodoLoadable(props) {
// react-redux state slice selector
const skip = useTodoSelector((state) => state.skip);
const limit = useTodoSelector((state) => state.limit);
const todoDispatch = useTodoDispatch();
// load data
useEffect(() => {
todoDispatch(setLoading('pending'));
api({ skip, limit })
.then((res) => todoDispatch({ todos: res.todos, total: res.total }))
.catch((e) => todoDispatch(setLoading('reject')));
}, [skip, limit]);
// render child
return <>{props.children}</>
}
The point to note here is that the loading logic is completely placed inside the loadable and the children can utilize the store to sync UI state accordingly. IsVisible
is a utility component that can be used to render things conditionally.
// [filename: IsVisible.utility.jsx]
function IsVisible({ visible, unmountOnExit, ...props }) {
if (unmountOnExit && !visible) {
return null;
}
return <div {...props} style={{ ...props.style, display: visible ? 'flex' : 'none' }} />
}
We can use the IsVisible
utility component to create state synced UI.
// [filename: Todo.jsx]
const Error = () => <div><h1>Error</h1></div>;
const Loader = () => <CircularProgress size="small" />
const Todos = () => {
const todos = useTodoSelector((state) => state.todos);
return <div>{todos.map((todo) => <h1>{todo}</h1>)}</div>
}
function IsErrorVisible(props) {
const isError = useTodoSelector((state) => state.status === 'reject');
return <IsVisible {...props} visible={isError} />
}
....more IsVisible for all API status 'reject' | 'resolve' | 'pending' | 'idle'
Now with the help of this IsVisible
, we can render UI according to the state of API.
// [filename: App.js]
const App = () => (
<div>
<TodoStoreProvider>
{/* Loadable holds all data loading logic*/}
<TodoLoadable>
<IsErrorVisible><ErrorUI /></IsErrorVisible>
<IsTodoVisible><Todos /></IsTodoVisible>
<IsLoaderVisible><Loader /></IsLoaderVisible>
</TodoLoadable>
</TodoStoreProvider>
</div>
);
This is how loadable
along with IsVisible
utility makes it super easy to load data in react and make a code simple to write and understand. Here is a link to demo Codesandbox.
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