In this section, we will be exploring how to implement the CRUD actions using the Redux pattern. To start, in this lesson and the next, we will revisit our todo app, building it out from scratch. This will allow us to review React and Redux concepts and to implement the create action.

By the end of this lesson, you will be able to:

• Take user input from our React todo application and send the information to Redux

We'll build a form using React and Redux that allows us to create a list of todos. Our form will be quite simple, consisting of a single input for the todo and a submit button.

In App.js you can see that we are rendering a CreateTodo component which is imported from the components/todos folder; the CreateTodo component is where we will build our form. If you boot up the application (run npm install && npm start), you'll see the text that is currently being rendered in the CreateTodo component.

To build our form, let's update the code in the CreateTodo component, replacing the text with a form element:

<form>
  <input type="text" placeholder="add todo" />
  <input type="submit" />
</form>

You should now see our form being rendered in the browser.

Now let's think about how we want to integrate this into Redux. Essentially, upon submitting the form, we would like to dispatch the following action to the store:

{
  type: 'ADD_TODO',
  todo: todo
}

So if the user has typed in "buy groceries", our action would look like:

{
  type: 'ADD_TODO',
  todo: 'buy groceries'
}

But how do we get that text from the form's input? Well, we can use our normal React trick of updating the createTodo component's state (not to be confused with the state in the Redux store) whenever someone types something into the form. Then, when the user clicks on the submit button, we can grab that state and use it to create our action:

{
  type: 'ADD_TODO',
  todo: this.state
}

Ok, time to implement it. Step one will be updating the component state whenever someone types in the form.

Every time the input is changed, we want to change the component state. To review, the process for doing this is:

1. create our initial component state; then
2. add an onChange handler to our input that calls a function which will...
3. use setState to update the component state whenever the user types something in the input field.

Let's start by setting the component's initial state:

// ./src/components/todos/createTodo

...

constructor() {
  super();
  this.state = {
    text: '',
  };
}

...

Next, we'll modify our render function, adding the event handler to our input element:

// ./src/components/todos/createTodo

...
render() {
  return(
    <div>
      <form>
        <input
          type="text"
          placeholder="add todo"
          onChange={(event) => this.handleChange(event)}
        />
        <input type="submit" />
      </form>
    </div>
  )
}

...

Finally, let's add our handleChange function:

// ./src/components/todos/createTodo

...

handleChange(event) {
  this.setState({
    text: event.target.value
  });
};

...

Notice that we pass through the event, which comes from the onChange event handler. The event's target is the input that was listening for the event (the text field), and the value is the current value of that text field.

Currently, we're using class method syntax to define handleChange() on our component. The JSX code within our render() method is particular to a specific instance of the component, but, by default, class methods are called in the context of the prototype chain, not in the context of an instance. In order for this to correctly reference this specific instance of our component, we need to either bind it (often done in the constructor()), or use an arrow function in our onChange event handler. Because arrow functions don't define their own version of this, they'll default to the context they are in.

In modern JavaScript, we are able to directly assign class properties instead of assigning them inside a constructor(). This means that, instead of writing handleChange() as a class method, we can declare it as a class property and assign an arrow function to it:

handleChange = (event) => {
  this.setState({
    text: event.target.value,
  });
};

The result is that handleChange() will always be bound to the particular instance of the component it is defined in. This means we can actually write an even shorter onChange callback: onChange={this.handleChange}. In this case, this.handleChange refers to the definition of a function that takes in the event as an argument. No need to explicitly pass event, which means no need for the onChange arrow function callback anymore!

To make a completely controlled form, we will also need to set the value attribute of our input element to this.state.text. This way, every key stroke within the input will call setState from within handleChange, and the component will re-render and display the new value for this.state.text.

With this final change, our CreateTodo component should look like this:

// ./src/components/todos/CreateTodo.js

import React, { Component } from "react";

class CreateTodo extends Component {
  constructor() {
    super();
    this.state = {
      text: "",
    };
  }

  handleChange = (event) => {
    this.setState({
      text: event.target.value,
    });
  };

  render() {
    return (
      <div>
        <form>
          <p>
            <input
              type="text"
              placeholder="add todo"
              onChange={this.handleChange}
              value={this.state.text}
            />
          </p>
          <input type="submit" />
        </form>
        {this.state.text}
      </div>
    );
  }
}

export default CreateTodo;

Note: As the user types, the text will show in the input box whether or not we have successfully controlled our form. To confirm that we are properly changing the component's state, we've added the line {this.state.text} at the bottom of the div wrapping our form. If we see our DOM change with every character we type in, we're in good shape.

It's on to step 2.

Okay, so now we need to make changes to our form so that when the user clicks submit, we dispatch an action to the store. Notice that a lot of the setup for Redux is already done for you. Open up the ./src/index.js file. There you'll see the following:

// ./src/index.js

import React from "react";
import ReactDOM from "react-dom";
import App from "./App";
import manageTodo from "./reducers/manageTodo";
import { Provider } from "react-redux";
import { createStore } from "redux";

let store = createStore(manageTodo);

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById("root")
);

Just below the import statements, you can see that we create the store using createStore, provided by redux. Then, further down, we pass the store into the Provider. This will allow us access to the store when we connect our c components.

Next we'll connect the CreateTodo component. First, we want to import connect from react-redux and modify our export statement:

// ./src/components/todos/CreateTodo.js
import { connect } from 'react-redux';

...

export default connect(null, mapDispatchToProps)(CreateTodo);

Note that we are passing null as the first argument to connect. This is because, for this component, we are not concerned with writing a mapStateToProps() function. In the next lesson, we will create components to render the todos and create a mapStateToProps function to access the todos in the store but, for now, the only thing we need from the store is the dispatch method. Since mapDispatchToProps must be passed as the second argument in order to have access to the dispatch method, we need to pass null as the first argument.

Next, as we write out our mapDispatchToProps() function, we'll need to decide how to structure our data and the related action. The basic frame of the function will look like the following:

// ./src/components/todos/CreateTodo.js

const mapDispatchToProps = (dispatch) => {
  return {
    addTodo: () => dispatch(someAction),
  };
};

From the Redux docs, we know that someAction needs to be a plain JavaScript object with a type key describing the type of action. We also need to include the data from the form - we'll call that key 'payload'.

const mapDispatchToProps = (dispatch) => {
  return {
    addTodo: () => dispatch({ type: "ADD_TODO", payload: formData }),
  };
};

Then, in order to make the form data available to our addTodo function, we'll pass it as an argument and access that value in our action object:

const mapDispatchToProps = (dispatch) => {
  return {
    addTodo: (formData) => dispatch({ type: "ADD_TODO", payload: formData }),
  };
};

Now we need to update the render() function of the CreateTodo component to call addTodo when the form is submitted. First we'll add the event handler to our form element:

// ./src/components/todos/CreateTodo.js

...

<form onSubmit={this.handleSubmit}>

...

Then we'll add the handleSubmit() function:

// ./src/components/todos/CreateTodo.js

...

handleSubmit = event => {
  event.preventDefault();
  this.props.addTodo(this.state)
}

...

When handleSubmit() is called, it in turn calls the addTodo function, passing in the form data stored in this.state as an argument. The addTodo function then creates the action and dispatches it to our reducer. The fully redux'd component ends up looking like the following:

import React, { Component } from "react";
import { connect } from "react-redux";

class CreateTodo extends Component {
  state = {
    text: "",
  };

  handleChange = (event) => {
    this.setState({
      text: event.target.value,
    });
  };

  handleSubmit = (event) => {
    event.preventDefault();
    this.props.addTodo(this.state);
  };

  render() {
    return (
      <div>
        <form onSubmit={this.handleSubmit}>
          <p>
            <input
              type="text"
              placeholder="add todo"
              onChange={this.handleChange}
              value={this.state.text}
            />
          </p>
          <input type="submit" />
        </form>
      </div>
    );
  }
}

const mapDispatchToProps = (dispatch) => {
  return {
    addTodo: (formData) => dispatch({ type: "ADD_TODO", payload: formData }),
  };
};

export default connect(null, mapDispatchToProps)(CreateTodo);

Now, if you start up the app and submit a todo, this.state will be dispatched to the reducer with the action. You should see your actions logged via a console.log in our reducer.

Remember that, if not given any arguments, connect will automatically return dispatch as a prop to the component we're wrapping with connect. Therefore, rather than creating a mapDispatchToProps function, we could instead call dispatch directly from our handleSubmit function, explicitly passing in our action:

...

  handleSubmit = (event) => {
    event.preventDefault();
    this.props.dispatch({ type: "ADD_TODO", payload: this.state });
  };

...

We would then also need to change our export as follows:

export default connect()(CreateTodo);

Now we are properly dispatching the action, but we haven't yet written the code in the reducer to update the state. So let's do that.

Open up the file ./src/reducers/manageTodo.js and you will see that the initial state is already set to an empty list of todos. Next, we need to update our reducer so it will add a new todo each time we receive an action. For example, if it receives an action that looks like { type: 'ADD_TODO', payload: { text: 'watch baseball' } }, our state should be updated to look like:

state = {
  todos: ["watch baseball"],
};

To do that, we will add a switch statement to our reducer that switches on our action type, and add a case for our ADD_TODO action. There we will use the spread operator to create a new list of todos in our state with the added todo at the end:

// ./src/reducers/manageTodo.js

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

      return { todos: [...state.todos, action.payload.text] };

    default:
      return state;
  }
}

With these changes, open up the console in your browser, and try adding a few todos. The log will show that our reducer is adding new values every time the form is submitted!

In the next lesson we will tackle rendering our list of todos to the DOM.

There's a lot of typing in this section, but three main steps.

• First, we made sure the React component of our application was working. We did this by building a form, and then making sure that whenever the user typed something into the form's input, the component's state was updated.

• Second, we connected the component to Redux and created our mapDispatchToProps to dispatch our ADD_TODO action to the reducer

• Third, we built our reducer such that it responded to the appropriate event and concatenated the payload into our array of todos.