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Load Data From a Server with fetch

4:19 React lesson by

We’ll fire up json-server so we can run our application against a server. We’ll take advantage of the fetch polyfill provided by create-react-app and leverage the componentDidMount lifecycle event to load our initial todo list. We’ll also add an error message to our UI in the case that the server is unavailable.

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We’ll fire up json-server so we can run our application against a server. We’ll take advantage of the fetch polyfill provided by create-react-app and leverage the componentDidMount lifecycle event to load our initial todo list. We’ll also add an error message to our UI in the case that the server is unavailable.

As it stands, the todos in this app are hard coded into the app's initial state and any changes are maintained in memory and lost when the application reloads. Let's integrate a server API for our todos so we can persist our updates.

To keep things simple, we'll be using the JSON server node module. I'll switch to my terminal and in a new tab, I'll install it globally using npmi -g json-server. With that installed, I'm going to go back into the editor and I'm going to add a new file at the root of my project. I'm going to call this db.json.

I'm just going to paste in some data. What we have here is a root object with a todos property, and todos is an array of todo objects. When we run JSON server, this will give us a todos endpoint that will give us access to these todo objects, so we can get them into our application and save changes back into this JSON file.

With some data in place, I'm going to switch back into the terminal and I'm going to start the server using json-server. I want to specify what port this is going to run on, so I'm going to use 8080. I also want it to reload if we manually make changes to db.json, so I'm going to pass it the watch flag.

Finally, I'm just going to pass in the name of our file, so it knows where to get its data from. I'll run that and we'll see that we now have a server running on local host 8080, and we have an endpoint called todos.

I just want to verify that it works, so I'm going to open another tab and I'm just going to run a curl against local host 8080/todos, and we'll see I get back my array of todo objects. Let's create a new file under lib. We'll call this todo-service.js. This is where we'll keep all of our code related to API calls.

I'm going to start with a constant, but I'm going to call base URL, and I'm going to set that to equal HTTP local host:8080/todos. The first thing I want to do with this API is use it to load the todos into the application when the application starts.

I'm going to export a function that I'm going to call load todos, and this function's going to return a call to fetch with our base URL. Fetch is going to return a response object. Since we want the JSON formatted data out of that, we're going to call .then, because we're going to get a promise back, and that's going to accept a response.

We're going to call response.json. That's going to return another promise with just the JSON formatted data. Now let's use our todo service in our app. I'm going to open up app.js, and up at the top, I'm going to add an import, and I'm going to import load todos from the flash todo service.

Since we're going to load our todos from the server, I'm going to take this initial todos array that was hard coded and we'll just start with our initial state, having an empty todos array. When the browser reloads, you'll see all of our todos are gone.

We want to call our load todos function when our component mounts. I'm going to drop down under this context types and I'll add the component did mount lifecycle method. Here I'm going to call load todos.

Load todos will return a promise, and since we already called the JSON method on the response in the load todos definition, this promise will resolve to our array of todos. This means I can call .then and I'm going to get back todos and I'm going to use that in a call to this.setState, and I'm going to pass this in.

Because my property name and my value name are the same, I can keep that short and just pass todos in curly braces. Now, when we save this, the browser should reload, and we should see the four tests that are defined in our db.json file show up in our application.

I'll save that, we'll let the browser reload, and our new tasks show up, so we know everything is working.

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