Adding An Item

Goals

  • Allow a user to create a new item.

  • Understand how to make an AJAX request when prompted by a user's action.

Overview

JavaScript allows us to make our web page dynamic, and responsive to the actions of our users. In this lesson, we'll allow our users to create a new item for our list, and ask the server to save it to the database.

To do so, we're going to use JavaScript's ability to perform a task when a user has taken an action on the page. JavaScript refers to these actions as events, and we can trigger code to run by using an event listener. We will be using jQuery to accomplish this, as it provides a powerful and readable interface to respond to user events.

Our code will take the following steps.

  1. When the user loads the page, our code will start listening for when the user submits the form at the top of the page.

  2. When a user submits the form (by pressing enter), we will prevent the page from refreshing, which is the normal behavior for a form.

  3. We will make an AJAX request to our server, creating an item with the description our user just provided.

  4. Once the request succeeds, we will add a new item to the page!

Steps

Step 1

Add the following code the bottom of app.js.

$('#add-form').on('submit', function(event) {
  var itemDescription = event.target.itemDescription.value
  alert('trying to create a new item with a description ' + itemDescription)
})

Refresh the page and try creating an item. An alert should pop up when you try! What happens after that? why?

Step 2

Before the alert we wrote in the last step, add the following line of code.

event.preventDefault()

Try creating an item again. What changed? Why did it change?

Step 3

Now that we've successfully listened for a form submission and prevented the page from refreshing, we're going to ask the server to save this item into the database. Remove the alert that you wrote in step one, and replace it with the following code. replace 'YOUR-LIST-NAME-HERE' with your list's name.

var creationRequest = $.ajax({
  type: 'POST',
  url: "http://listalous.herokuapp.com/lists/YOUR-LIST-NAME-HERE/items",
  data: { description: itemDescription, completed: false }
})

Try creating an item again. After you submit the form, look at the network tab. A new request should have occurred to http://listalous.herokuapp.com/ !

Step 4

Finally, we need to add the new item to the list. We'll use our addItemToPage function again to do so. After the creationRequest, add the following code:

creationRequest.done(function(itemDataFromServer) {
  addItemToPage(itemDataFromServer)
})

Try creating an item one more time. Once you hit enter, a new item should appear on the page! If not, flag an instructor down to help you debug the problem.

Explanation

Here's what the bottom of app.js should now look like:

$('#add-form').on('submit', function(event) {
  event.preventDefault()
  var itemDescription = event.target.itemDescription.value
  var creationRequest = $.ajax({
     type: 'POST',
     url: "https://listalous.herokuapp.com/lists/YOUR-LIST-NAME-HERE/items",
     data: { description: itemDescription, completed: false }
   })
  creationRequest.done(function(itemDataFromServer) {
    addItemToPage(itemDataFromServer)
  })
})

The AJAX process

You've just done something that many JavaScript developers do daily: Use JavaScript to make a request to a server, and then update the page with the data with which the server responds. This abstract process is repeated over and over again:

  1. Add an event listener.
  2. Parse out the information the user is submitting.
  3. Prevent the default action from occurring, if necessary.
  4. Make a request to the server using AJAX.
  5. When the request succeeds, parse the data the server sends back.
  6. Update the page with the newly received data.

This process is the basis of most modern web pages!

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