data() and Vue Dev Tools

The template I pasted in is 100% hardcoded. Boring!

See this little "shipping" message down here? Let's pretend that sometimes we need this message to change - like maybe if the user is on the page for longer than 60 seconds, we want our app to get desperate and change the shipping time to be faster.

The point is: we want this message to be dynamic, which means that it needs to to be a data. Copy the message. Then, in data(), remove firstName: we're not using that anymore. Call the new data key legend and set it to the shipping message.

Now that we have a data called legend, back up on the template, we're allowed to say {{ legend }}.

Beautiful! And if we move over to our browser and refresh... it even works!

Vue Dev Tools

The first time we played with data, we set our entire Vue application onto a global variable so we could change the firstName data from our browser's console and watch the HTML update. Being able to see and play with the data on your components is a pretty handy way to debug. And fortunately, there's a much easier way to do this than manually setting a global variable.

It's called the "Vue.js Dev Tools": a browser extension for Chrome or Firefox that gives you tons of Vue information. If you don't already have it, install it - it's amazing.

Once you have the dev tools... and once you're on a page that contains a Vue app running in dev mode, you can open your browser's debugging tools - I actually need to close and re-open mine so that it sees my Vue app - and... boom! New Vue tab. Click it!

I love this. On the left, it shows the component "hierarchy" of my app. In a few minutes, we're going to create more components and start nesting them inside of each other, just like HTML. If you click on <Products>, ah: on the right, you can see the data for this component. And we can change its value! Add quotes and replace this with whatever message is in your heart. When you hit the save icon... the HTML updates! Vue calls this "reactivity": the idea that Vue watches your data for changes and re-renders a component when necessary.

Anyways, the Vue dev tools will be a powerful way to visualize our app, see its data and even change data to see how things update.

The data() Function versus data: () => { Function

Before we create our second component, I need to point out a small detail. We configure Vue by passing it options. Some of these options are set directly to values, while others - like data() - are functions.

And because the data() function is always just a return statement, you'll often see it written with the shortcut, arrow syntax: data: (), arrow, ({, remove the return and fix the ending.

Just like with the render shortcut we used in products.js, this is effectively the same: it says that the data property is set to a function that returns this object. The return is implied.

You can use this if you want... but I'm going to go back to the original way. It's a bit longer, but I'll use this syntax consistently for all Vue options that are set to functions. The shorter syntax also has a limitation where you can't use the this variable: something that we will need later.

Next: let's extract part of our product listing markup into a second component and include it from Products. This will start to show off one of Vue's key concepts: having multiple components that communicate to each other.