如何通过客户端JS从Outlook加载项获取邮件及附件并上传至SharePoint？

Great question! Let's walk through how to build this Outlook add-in using client-side JavaScript, minimizing server-side code as requested:

First, you'll rely on the official Office.js library (built into Outlook add-ins) to fetch email data. Here's how to do it:

• Permissions Setup: Make sure your add-in manifest has the right permissions (e.g., ReadWriteMailbox or at least ReadMailbox) to access email content and attachments.
• Fetch Email Metadata: Use Office.context.mailbox.item to access core email details like subject, body, or sender:

  const currentEmail = Office.context.mailbox.item;
  console.log("Email Subject:", currentEmail.subject);
  console.log("Sender:", currentEmail.sender.emailAddress);
  

• Retrieve Attachments: Loop through the attachments collection, and use getAsync to pull file content (returned as an ArrayBuffer):

  currentEmail.attachments.forEach(attachment => {
    if (attachment.attachmentType === Office.MailboxEnums.AttachmentType.File) {
      attachment.getAsync((asyncResult) => {
        if (asyncResult.status === Office.AsyncResultStatus.Succeeded) {
          const attachmentBuffer = asyncResult.value;
          // Convert to Blob for upload: const attachmentBlob = new Blob([attachmentBuffer]);
        }
      });
    }
  });
  

Office.js has direct support for .eml, while .msg requires a workaround since it's an Outlook-proprietary format:

• .eml Export: This is straightforward—use getAsync with the Eml content format to fetch the full MIME-compliant eml string:

  currentEmail.getAsync(Office.MailboxEnums.ItemContentFormat.Eml, (asyncResult) => {
    if (asyncResult.status === Office.AsyncResultStatus.Succeeded) {
      const emlContent = asyncResult.value;
      // Convert to Blob for storage/upload:
      const emlBlob = new Blob([emlContent], { type: 'message/rfc822' });
    }
  });
  

• .msg Export: There's no native Office.js API to get raw .msg content. If you absolutely need .msg, you could look for a pure JavaScript library that generates .msg files from email data (but be cautious about add-in security restrictions for external libraries). For most use cases, .eml is a more portable and easier-to-implement alternative.

You can use SharePoint's REST API directly from your add-in, no server-side code needed, by leveraging the user's existing authentication context:

• Get Access Token: Use Office.js's SSO capability to fetch a bearer token for SharePoint requests:

  Office.context.auth.getAccessTokenAsync({ allowSignInPrompt: true }, (authResult) => {
    if (authResult.status === Office.AsyncResultStatus.Succeeded) {
      const accessToken = authResult.value;
      uploadToSharePoint(accessToken, emlBlob, currentEmail.subject + ".eml");
    }
  });
  

• Upload File Function: Call SharePoint's file upload endpoint with the blob content:

  function uploadToSharePoint(token, fileBlob, fileName) {
    const spSiteUrl = "https://your-sharepoint-site-url/_api/web/getfolderbyserverrelativeurl('Documents')/files/add(overwrite=true,url='${encodeURIComponent(fileName)}')";
    
    fetch(spSiteUrl, {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${token}`,
        'Accept': 'application/json;odata=nometadata'
      },
      body: fileBlob
    })
    .then(res => res.json())
    .then(data => {
      console.log("Upload successful!", data);
      // Show success message to user here
    })
    .catch(err => console.error("Upload failed:", err));
  }
  

• Permissions Note: Ensure your add-in manifest includes WebApplicationInfo settings for SSO, so users can grant access to your SharePoint site without extra login prompts.

• Cross-Client Compatibility: Test your add-in across Outlook Web, desktop, and mobile—some API features may have slight platform differences.
• Large Files: For big attachments or emails, consider implementing chunked uploads via SharePoint's REST API to avoid timeouts.
• Security: Stick to Office.js's official APIs and avoid untrusted third-party libraries to keep your add-in compliant with Office store policies.

内容的提问来源于stack exchange，提问作者Paddy P