What's the purpose of Vuex?

There are a lot of things to worry about when it comes to Vue applications. You've got SPAs and routing and web workers and Jest and Cypress and everything else. It gets overwhelming pretty quickly. The hard part is not learning these technologies, it's knowing what their place is in the application.

So, Vuex. What the heck is it for and why might you want to use it?

To start with, let me tell you what its function is. Vuex is a Vue addon that acts as a central data store to all the parts of your front-end application. A Vue application is composed of a lot of separate but coordinated components that, when put together, create a functioning front-end application. You might have a screen to edit users, a screen to show users, a screen to show a specific user and they all need to work together and communicate with each other to be in a useful way. Vuex can help do that by keeping all that data in one place and allowing all of these separate components to access and change it.

And that's what Vuex can do. So what is Vuex?

Vuex is a front-end datastore

Vuex is a datastore that is used by all the components in an application to share data. When a component creates data, it can put it into Vuex so that other components can use it. If a component displays or uses data from Vuex, it will be updated immediately if that data ever gets updated. In other words, its data is reactive.

Vuex acts as a central place for data to live. This doesn't mean that all data goes there. If there really is data that's only used by a single component, that component can still have data properties all its own. But if the same data needs to be synced across multiple components, that's where Vuex comes in.

Vuex is a single source of truth

You'll see this often in the documentation. What does single source of truth mean?

I mentioned "synced across multiple components" before and that's exactly what you don't want to do. You don't want copies of data in each component that you have to keep in sync between components. Imagine having each component having their own data properties that, when one changes, you had to somehow let all the others know that it changed and then copying that data between all the components. (Please don't ever do that.)

Vuex acts as the single source to go for data. If every component knows to keep and get data in Vuex instead of individually and treat it as the source of data, that greatly simplifies your application.

Vuex is not a database

Nothing in Vuex is meant to be permanent. Vuex is not your database and you should not load your entire database into Vuex! Vuex is simply there to hold data that the user needs right now. Front-ends should be fast and light, so only keep in the Vuex store what the user is currently interested in seeing. If they need new information, clear the current stuff and load in the information from a separate permanent storage. And if something changes and needs to be saved to the permanent store, do that right away. Don't wait because Vuex won't stick around if someone leaves the page or the app crashes.

You might be wondering about offline abilities. Shouldn't you load things into Vuex so the user can work offline?

No. That's what Window.localStorage or IndexedDB API is for. You can tie your Vuex store to these more permanent datastores, but Vuex does not replace them. Vuex is always temporary data that your components are using right now.

So what's the purpose of Vuex? To simplify your Vue application's data handling. It's there to keep all your runtime data in one place and accessible to all the components in your application. If you can learn to use this powerful tool, you're going to make your work a whole lot easier to code and maintain.