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Exercise - Load a user's emails in batches

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In this exercise, you'll extend the app to let you load a user's emails in batches of 10 items.

Load emails in batches of 10 items

Start by updating the getEmails() function to load emails in batches of 10 items. If the next set of emails to load has been defined, it's passed as the function's argument.

1. In your code editor, open the graph.js file.

2. Update the getEmails() function's signature to accept a single argument nextLink:

   async function getEmails(nextLink) {
     // ...
   }
   

3. If the nextLink has been set, the function should pass it to the SDK to retrieve the data. If nextLink hasn't been set, the function should load the initial set of data. Update the getEmails() function by replacing the return statement with the following if statement:

   if (nextLink) {
     return await graphClient
       .api(nextLink)
       .get();
   }
   else {
     return await graphClient
       .api('/me/messages')
       .select('subject,receivedDateTime')
       .orderby('receivedDateTime desc')
       .top(10)
       .get();
   }
   

   The updated getEmails() function should look as follows:

   async function getEmails(nextLink) {
     ensureScope('mail.read');
   
     if (nextLink) {
       return await graphClient
         .api(nextLink)
         .get();
     }
     else {
       return await graphClient
         .api('/me/messages')
         .select('subject,receivedDateTime')
         .orderby('receivedDateTime desc')
         .top(10)
         .get();
     }
   }
   

Extend the template to allow users to load more emails

You've extended the getEmails() function to load more emails. The next step is to show a button that will let users load more emails if available.

1. In your code editor, open the index.html file.

2. Locate the line <ul id="emails"></ul> and add the following code immediately after it to add a button that allows users to load more emails.

   <div id="loadMoreContainer" style="display: none;">
     <button onclick="displayEmail();">Load more</button>
   </div>
   

Load more emails

With the app updated to let users load more emails, the final step is to add functionality to handle loading more emails.

1. In your code editor, open the ui.js file.

2. Before the displayEmail() function, define a new variable named nextLink without assigning a value to it:

   var nextLink;
   

3. In the displayEmail() function, update the call to get the getEmails() function to include the nextLink.

   var emails = await getEmails(nextLink);
   

4. Next, after retrieving the data, get the value of the @odata.nextLink property. If set, it will indicate that there's more data available for users to show. Add the following code immediately after the if statement in the displayEmail() function:

   nextLink = emails['@odata.nextLink'];
   

5. At the end of the displayEmail() function, after displaying the retrieved emails, scroll to the end of the page so that the user can immediately see the retrieved emails.

   window.scrollTo({ top: emailsUl.scrollHeight, behavior: 'smooth' });
   

6. Finally, check if nextLink has been returned and if so, display the button to load more emails.

   Add the following code to the end of the displayEmail() function:

   if (nextLink) {
     document.getElementById('loadMoreContainer').style = 'display: block';
   }
   

7. The complete displayEmail() function should look as follows:

   var nextLink;
   async function displayEmail() {
     var emails = await getEmails(nextLink);
     if (!emails || emails.value.length < 1) {
       return;
     }
     nextLink = emails['@odata.nextLink'];
   
     document.getElementById('displayEmail').style = 'display: none';
   
     var emailsUl = document.getElementById('emails');
     emails.value.forEach(email => {
       var emailLi = document.createElement('li');
       emailLi.innerText = `${email.subject} (${new Date(email.receivedDateTime).toLocaleString()})`;
       emailsUl.appendChild(emailLi);
     });
     window.scrollTo({ top: emailsUl.scrollHeight, behavior: 'smooth' });
   
     if (nextLink) {
       document.getElementById('loadMoreContainer').style = 'display: block';
     }
   }
   

Run your app

You've extended your app to show a user's emails by using Microsoft Graph in batches of 10 items and let them load more emails. Let's run the app locally.

1. Preview the web app by executing the following command in the terminal.

   npm start
   

2. Your browser should be pointing to http://localhost:8080.

3. Select the Sign in with Microsoft button to sign in with your Microsoft 365 account.

4. After you sign in with your account, select the Show email button.

5. You should see a list of the user's last 10 emails displayed in the app.

6. If there are more than 10 emails in your mailbox, you'll see a button that allows you to load the next 10 messages.

7. Stop the Node.js server by selecting CTRL+C in the terminal window.

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