using connect's mapToProps vs reading and dispatching to the store as a global?

Question

What's the difference between A) using the connect method of connecting state and dispatch function to a component and B) simply having functions in a component that do the dispatching as well as accessing the store as a global directly?

(Not ES2015)

Answer 1

Quoting from the Redux FAQ on importing the store directly:

While you can reference your store instance by importing it directly, this is not a recommended pattern in Redux. If you create a store instance and export it from a module, it will become a singleton. This means it will be harder to isolate a Redux app as a component of a larger app, if this is ever necessary, or to enable server rendering, because on the server you want to create separate store instances for every request.

I also recently wrote a Reddit comment on why you should use React-Redux and connect instead of talking to the store directly. Quoting that:

First, while you can manually write the code to subscribe to the Redux store in your React components, there's absolutely no reason to write that code yourself. The wrapper components generated by React-Redux's connect function already have that store subscription logic taken care of for you.

Second, connect does a lot of work to ensure that your actual components only re-render when they actually need to. That includes lots of memoization work, and comparisons against the props from the parent component and the values returned by your mapStateToProps function for that component. By not using connect, you're giving up all those performance improvements, and your components will be unnecessarily re-rendering all the time.

Third, by only connecting your top-level component, you are also causing the rest of your app to re-render unnecessarily. The best performance pattern is to connect lots of components in your app, with each connected component only extracting the pieces of data it actually needs via mapStateToProps. That way, if any other data changes, that component won't re-render.

Fourth, you're manually importing the store into your components, and directly coupling them together, thus making it harder to test the components. I personally try to keep my components "unaware" of Redux. They never reference props.dispatch, but rather call pre-bound action creators like this.props.someFunction(). The component doesn't "know" that it's a Redux action creator - that function could be a callback from a parent component, a bound-up Redux action creator, or a mock function in a test, thus making the component more reusable and testable.

And finally, the vast majority of apps built using React and Redux use the React-Redux library. It's the official way to bind the two together, and doing anything else will just confuse other developers looking at your project.

For more info, see:

• The Redux FAQ section on performance
• The Redux FAQ entry on connecting multiple components
• The Redux FAQ entry on components re-rendering too often
• The Redux FAQ entry on importing the store directly
• The Redux Performance section of my React/Redux links list
• And finally, my blog posts Practical Redux, Part 6: Connected Lists, Forms, and Performance and Idiomatic Redux: Why use action creators?.

Source: I'm a Redux maintainer, and author of the Redux FAQ.