learn-co-students/redux-delete-codealong-nyc-web-060418

Deleting Items with Redux

Objectives

With this lesson we'll continue through our journey through Redux. By the end of this lesson, you will be able to:

• Delete individual elements

Review and Goal

Throughout each code along in this section, notice that we are never updating the DOM directly. Instead, we use the Redux pattern to have our store hold and update our state, and we then have React display that state. We want to continue with this pattern here.

Our goal this timeis to have a button next to each list element with the todo; such that when a user clicks on that button, the list element will be removed. In implementing this, remember that the Todos component displays the current list of todos, if we remove a todo from the store's state, the display of that todo should be removed.

Deleting A Todo

To delete a todo we should add a button that when clicked, dispatches an action telling the store to delete a specific todo. How we tell the store which todo to delete, we'll figure out at the end. For now let's add in the button, and have it call a method that dispatches a delete action when clicked.

Modifying our TodosContainer

Sticking with our container vs presentational set up, we don't want to load our presentational Todo component up with logic. Meanwhile, TodosContainer is where we're connected to Redux, so let's write in a new mapDispatchToProps() function to include an action:

// ./src/components/todos/TodosContainer.js
import React, { Component } from 'react';
import { connect } from 'react-redux'
import Todo from './Todo'

class TodosContainer extends Component {

  renderTodos = () => this.props.todos.map((todo, id) => <Todo key={id} text={todo} />)

  render() {
    return(
      <div>
        {this.renderTodos()}
      </div>
    );
  }
};

const mapStateToProps = state => {
  return {
    todos: state.todos
  }
}

const mapDispatchToProps = dispatch => {
  return {
    delete: todoText => dispatch({type: 'DELETE_TODO', payload: todoText })
  }
}

export default connect(mapStateToProps, mapDispatchToProps)(TodosContainer);

Now, TodosContainer will have access to this.props.delete, which can take in an argument and send it as the action's payload. We can then pass this.props.delete down to Todo, so that each Todo component rendered will have access to our 'DELETE_TODO' action.

renderTodos = () => this.props.todos.map((todo, id) => <Todo delete={this.props.delete} key={id} text={todo} />)

Modifying the Todo Component

Todo is receiving this.props.delete, so let's update the component a little and incorporate a button:

import React from 'react'

const Todo = props => {
  return (
    <div>
      <span>{props.text}</span><button>DELETE</button>
    </div>
  )
}

export default Todo;

When we click the button we want to be able to delete this particular todo. At the moment, our todos are just strings, stored in an array. Since that is all we have to work with, we add an onClick attribute to the new button. To keep this component small, we can provide an anonymous function in-line:

<div>
  <span>{props.text}</span><button onClick={() => props.delete(props.text)}>DELETE</button>
</div>

So, what is happening here? We're providing a definition for an anonymous function. Inside the definition, we're calling props.delete, and passing in the only other prop available, props.text.

Back in our connected TodosContainer, when this delete button is clicked, the value of props.text is passed into our dispatched action as the payload.

There is a console.log in our reducer that displays actions. Clicking the delete button should log an action with the todo's text content as the payload.

Ok, now we have the ability to dispatch an action to the reducer from each Todo!

Tell the Store Which Todo to Delete

Our todos are stored as strings in an array. There are a number of ways to remove a specific string from an array, but one of the more brief options is to use filter. By adding a second case to our manageTodo reducer, we can write a filter that returns every todo that doesn't match what is contained in action.payload:

export default function manageTodo(state = {
  todos: [],
}, action) {
  console.log(action);
  switch (action.type) {
    case 'ADD_TODO':

      return { todos: state.todos.concat(action.payload.text) };

    case 'DELETE_TODO':

      return {todos: state.todos.filter(todo => todo !== action.payload)}

    default:
      return state;
  }
}

In our browser, the delete button should now successful cause todos to disappear!

There is a problem though. What if you have multiple todos with the same text? With this set up, every todo that matches action.payload will be filtered out.

To get around this, instead of filtering just text, it would be better if we gave our Todos specific IDs.

Give each Todo an id

A Todo should have an id the moment it gets created. So, we know that our reducer creates the Todo when a CREATE_TODO action is dispatched. Let's update the code in there so that it also adds an id.

// ./src/reducers/manageTodo.js

export default function manageTodo(state = {
  todos: [],
}, action) {
  console.log(action);
  switch (action.type) {
    case 'ADD_TODO':

      const todo = {
        id: Math.random()*10000000000000000,
        text: action.payload.text
      }
      return { todos: state.todos.concat(todo) };

    case 'DELETE_TODO':

      return {todos: state.todos.filter(todo => todo !== action.payload)}

    default:
      return state;
  }
}

Using Math.random()*10000000000000000 will generate a long random number each time a todo is created. Now, instead of just storing an array of strings, we'll be storing an array of objects.

This causes a problem 'downstream', though: we need to update our TodosContainer to pass the correct content.

Update TodosContainer

In TodosContainer, our renderTodos method will need to change a little:

renderTodos = () => {
  return this.props.todos.map(todo => <Todo delete={this.props.delete} key={todo.id} todo={todo} />)
}

The change is minimal, but this set up is actually better. Previously, key was based off the index provided by map. Now its using our randomly generated ID, and is less prone to errors in the virtual DOM. We'll need both todo.id and todo.text to be passed into Todo so we pass both down as the object, todo.

Update the Todo Component

Now that we've got todo.id, we can modify the Todo component to use props.todo.id on click:

import React from 'react'

const Todo = props => {
  return (
    <div>
      <span>{props.todo.text}</span><button onClick={() => props.delete(props.todo.id)}>DELETE</button>
    </div>
  )
}

export default Todo;

Now, when props.delete is called, an action is dispatched that contains an id only as its payload.

Updating DELETE_TODO in the Reducer

Now that we're passing an id to props.delete, we need to modify our reducer once more:

case 'DELETE_TODO':

  return {todos: state.todos.filter(todo => todo.id !== action.payload)}

Instead of comparing todo with action.payload, now that todo is an object, we want to match todo.id with the payload.

With this final change, todo objects can be added and deleted, each with their own unique id!

Summary

Ok, so in this lesson we covered how to delete a specific Todo. To implement this, we gave each Todo a unique id, and then made sure we passed that id into each Todo component. Then we made sure to send along that information when dispatching an action via props.delete. Finally, we had our reducer update the state by filtering out the Todo to be deleted.