Dispatch an action in a React component

How to connect a React component to action creator

We have seen how to connect a component to an action creator through the connect function made available by the React Redux library.

But connecting a component to an action creator is not enough. In order to actually trigger the action we need to listen to an event and fire up a function that calls the action creator that we have connected.

Since we passed the action creator to connect, this function is now available to the component through the props.
Here's the relevant code we put at the bottom of our Title component file:

export default connect(
  () => {},
  { turnTitleGreen }
)(Title);

In this case, the action creator is turnTitleGreen and we pass it to connect inside the object in the second argument.
This syntax:

{ turnTitleGreen }

is equivalent to saying this:

{turnTitleGreen: turnTitleGreen}

So, we effectively created a property on this object. The property is called turnTitleGreen and the value is the turnTitleGreen function that was imported from actions/index.js

The connect function sets things up so our Title component now has a prop called turnTitleGreen, set to the value of the action creator.
This means that we can invoke the action creator like this:

this.props.turnTitleGreen();

and the action creator will be called, and will dispatch the appropriate action to the reducer.

How do we invoke turnTitleGreen, though?
Let's say we want to turn the title green when someone clicks a button.
We add an event handler to the button with the onClick property pointing to
a function in the component:
Here's the button:

<button onClick={this.handleTitleGreen}>Change title color</button>

Now we need to define the handleTitleGreen inside our component:

handleTitleGreen = e => {
  e.preventDefault();
  this.props.turnTitleGreen();
}

We have seen these type of functions before. First we prevent default, so the page won't be reloaded as a result of clicking the button.
Then we call the turnTitleGreen function that lives on the props.
This sends the TURN_TITLE_GREEN action to the reducer and the reducer returns a new state object with the titleColor property changed to 'green'.

In Title, the actual title is inside an h1 component. h1 has a style property with the text color set to the value of the titleColor property on the state. When the reducer changes this property, the text color gets updated accordingly.

<h1 style={{ color: this.props.titleColor }} >
  This is the title
</h1>

And with this we have come full loop: we click a button that triggers an event.
The event calls a function that calls an action creator.
The action creator dispatches an action that ultimately changes the title in our component.


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