[Redux] Fetching Data on Route Change

We will learn how to fire up an async request when the route changes.

A mock server data:

/** /api/index.js
 * Created by wanzhen on 7.6.2016.
 */
import { v4 } from 'node-uuid';

// This is a fake in-memory implementation of something
// that would be implemented by calling a REST server.

const fakeDatabase = {
    todos: [{
        id: v4(),
        text: 'hey',
        completed: true,
    }, {
        id: v4(),
        text: 'ho',
        completed: true,
    }, {
        id: v4(),
        text: 'let’s go',
        completed: false,
    }],
};

const delay = (ms) =>
    new Promise(resolve => setTimeout(resolve, ms));

export const fetchTodos = (filter) =>
    delay(500).then(() => {
        switch (filter) {
            case 'all':
                return fakeDatabase.todos;
            case 'active':
                return fakeDatabase.todos.filter(t => !t.completed);
            case 'completed':
                return fakeDatabase.todos.filter(t => t.completed);
            default:
                throw new Error(`Unknown filter: ${filter}`);
        }
    });

We want to replace localStorge with mock server data, so remove the localStorge code:

// configureStore.js

import { createStore } from 'redux';
import todoApp from './reducers';

const addLoggingToDispatch = (store) => {

    const rawDispatch = store.dispatch;

    // If browser not support console.group
    if (!console.group) {
        return rawDispatch;
    }

    return (action) => {
        console.group(action.type);
        console.log('%c prev state', 'color: gray', store.getState());
        console.log('%c action', 'color: blue', action);
        const returnValue = rawDispatch(action);
        console.log('%c next state', 'color: green', store.getState());
        console.groupEnd(action.type);
        return returnValue;
    };
};

const configureStore = () => {
    const store = createStore(todoApp);

    // If in production do not log it
    if (process.env.NODE_ENV !== 'production') {
        store.dispatch = addLoggingToDispatch(store);
    }

    return store;
};

export default configureStore;

We want to fetch data inside the component: VisibleTodoList.js.

The good place to fetch data is in 'componentDidMount' lifecycle: This will fetch the initial data, which only run once.

Thats not enough, we still need when the filter changes, it also need to fetch data, for that we can use another lifecycle 'componentDidUpdate'.

import {connect} from 'react-redux';
import {toggleTodo} from '../actions';
import TodoList from './TodoList';
import {withRouter} from 'react-router';
import {getVisibleTodos} from '../reducers';
import  React, {Component}  from 'react';
import {fetchTodos} from '../api';


class VisibleTodoList extends Component {

    // Fetch data when component mount
    componentDidMount() {
        fetchTodos(this.props.filter)
            .then((todos) => {
                console.log(this.props.filter, todos);
            })
    }

    // Check the filter props, when it changes, fetch data again
    componentDidUpdate(prevProps) {
        if (this.props.filter !== prevProps.filter) {
            fetchTodos(this.props.filter)
                .then((todos) => {
                    console.log(this.props.filter, todos);
                })
        }
    }

    render() {
        return (
            <TodoList {...this.props}/>
        )
    }
}

const mapStateToProps = (state, {params}) => {
    const filter = params.filter || 'all';
    //todos, filter Will available in props
    return {
        todos: getVisibleTodos(state, filter),
        filter, 
    };
};

//re-assign the VisibleTodoList
VisibleTodoList = withRouter(connect(
    mapStateToProps,
    {onTodoClick: toggleTodo}
)(VisibleTodoList));

export default VisibleTodoList;