Tutorial: Enable file attachment support in your Chat app

The Chat SDK is designed to work with Microsoft Teams seamlessly. Specifically, Chat SDK provides a solution to receive file attachments sent by users from Microsoft Teams. Currently this feature is only available in the Chat SDK for JavaScript. Please note that sending file attachments from Azure Communication Services user to Teams user is not currently supported, see the current capabilities of Teams Interop Chat for details.


This feature of Azure Communication Services is currently in preview.

Preview APIs and SDKs are provided without a service-level agreement. We recommend that you don't use them for production workloads. Some features might not be supported, or they might have constrained capabilities.

For more information, review Supplemental Terms of Use for Microsoft Azure Previews.

Add file attachment support

The Chat SDK for JavaScript provides previewUrl for each file attachment. Specifically, the previewUrl provides a link to a webpage on the SharePoint where the user can see the content of the file, edit the file and download the file if permission allows.

You should be aware of couple constraints that come with this feature:

  1. The Teams admin of the sender's tenant could impose policies that limits or disable this feature entirely. For example, the Teams admin could disable certain permissions (such as "Anyone") that could cause the file attachment URLs (previewUrl) to be inaccessible.

  2. We currently only support the following file permissions:

    • "Anyone", and
    • "People you choose" (with email address)

    The Teams user should be made aware of that all other permissions (such as "People in your organization") aren't supported. The Teams user should double check if the default permission is supported after uploading the file on their Teams client.

  3. The direct download URL (url) is not supported.

In addition to regular files (with AttachmentType of file), the Chat SDK for JavaScript also provides the AttachmentType of teamsImage for image attachments so that you can use it to mirror the behavior of how Microsoft Teams client converts image attachment to inline images in the UI layer. See section "Image Attachment Handling" for more info.

Note that images added via "Upload from this device" renders on Teams side, and Chat SDK for JavaScript would be returning such attachments as teamsImage. For images uploaded via "Attach cloud files" however, they would be treated as regular files on the Teams side, and therefore Chat SDK for JavaScript would be returning such attachments as file.

Also note that only files uploaded via "drag-and-drop" or via attachment menu of "Upload from this device" and "Attach cloud files" are supported. Some messages with embedded media (such as video clips, audio messages, weather cards, etc.) are adaptive card, which currently isn't supported.

In this tutorial, you learn how to enable file attachment support using the Azure Communication Services Chat SDK for JavaScript.

Sample code

Find the finalized code of this tutorial on GitHub.


  • You've gone through the quickstart - Join your chat app to a Teams meeting.
  • Create an Azure Communication Services resource. For details, see Create an Azure Communication Services resource. You need to record your connection string for this tutorial.
  • You've set up a Teams meeting using your business account and have the meeting URL ready.
  • You're using the Chat SDK for JavaScript (@azure/communication-chat) 1.3.2-beta.2 or the latest. See here.


  1. Be able to render file attachment in the message thread. Each file attachment card has an "Open" button.
  2. Be able to render image attachments as inline images.

Handle file attachments

The Chat SDK for JavaScript would return AttachmentType of file for regular files and teamsImage for image attachments.

export interface ChatMessageReceivedEvent extends BaseChatMessageEvent {
   * Content of the message.
  message: string;

   * Chat message attachment.
  attachments?: ChatAttachment[];

export interface ChatAttachment {
  /** Id of the attachment */
  id: string;
  /** The type of attachment. */
  attachmentType: AttachmentType;
  /** The type of content of the attachment, if available */
  contentType?: string;
  /** The name of the attachment content. */
  name?: string;
  /** The URL that is used to provide original size of the inline images */
  url: string;
  /** The URL that provides the preview of attachment */
  previewUrl?: string;

/** Type of Supported Attachments. */
export type AttachmentType = "teamsInlineImage" | "teamsImage" | "file";

As an example, the following JSON is an example of what ChatAttachment might look like for an image attachment and a file attachment:

"attachments": [
        "id": "08a182fe-0b29-443e-8d7f-8896bc1908a2",
        "attachmentType": "file",
        "contentType": "pdf",
        "name": "business report.pdf",
        "url": "",
        "previewUrl": "https://contoso.sharepoint.com/:u:/g/user/h8jTwB0Zl1AY"
        "id": "9d89acb2-c4e4-4cab-b94a-7c12a61afe30",
        "attachmentType": "teamsImage",
        "contentType": "png",
        "name": "Screenshot.png",
        "url": "https://contoso.communication.azure.com/chat/threads/19:9d89acb29d89acb2@thread.v2/messages/123/teamsInterop/images/9d89acb2-c4e4-4cab-b94a-7c12a61afe30/views/original?api-version=2023-07-01-preview",
        "previewUrl": "https://contoso.communication.azure.com/chat/threads/19:9d89acb29d89acb2@thread.v2/messages/123/teamsInterop/images/9d89acb2-c4e4-4cab-b94a-7c12a61afe30/views/small?api-version=2023-07-01-preview"

Now let's go back to event handler we have created in previous quickstart to add some extra logic to handle attachments with attachmentType of file:

chatClient.on("chatMessageReceived", (e) => {
  console.log("Notification chatMessageReceived!");
  // check whether the notification is intended for the current thread
  if (threadIdInput.value != e.threadId) {
  if (e.sender.communicationUserId != userId) {
  } else {

async function renderReceivedMessage(event) {
    messages += `<div class="container lighter"> ${event.message} </div>`;
    messagesContainer.innerHTML = messages;

    // get list of attachments and calls renderFileAttachments to construct a file attachment card
    var attachmentHtml = event.attachments
        .filter(attachment => attachment.attachmentType === "file")
        .map(attachment => renderFileAttachments(attachment))
    messagesContainer.innerHTML += attachmentHtml;

function renderFileAttachments(attachment) {
    return '<div class="attachment-container">' +
        '<p class="attachment-type">' + attachment.contentType + '</p>' +
        '<img class="attachment-icon" alt="attachment file icon" />' +
        '<div>' +
        '<p>' + attachment.name + '</p>' +
        '<a href=' + attachment.previewUrl + ' target="_blank" rel="noreferrer">Open</a>' +
        '</div>' +

Let's make sure we add some CSS for the attachment card as well:

  /* let's make chat popup scrollable */
  .chat-popup {


     max-height: 650px;
     overflow-y: scroll;

 .attachment-container {
     overflow: hidden;
     background: #f3f2f1;
     padding: 20px;
     margin: 0;
     border-radius: 10px;
 .attachment-container img {
     width: 50px;
     height: 50px;
     float: left;
     margin: 0;
 .attachment-container p {
     font-weight: 700;
     margin: 0 5px 20px 0;
 .attachment-container {
     display: grid;
     grid-template-columns: 100px 1fr;
     margin-top: 5px;
 .attachment-icon {
     content: url("data:image/svg+xml;base64, ...");
 .attachment-container a {
     background-color: #dadada;
     color: black;
     font-size: 12px;
     padding: 10px;
     border: none;
     cursor: pointer;
     border-radius: 5px;
     text-align: center;
     margin-right: 10px;
     text-decoration: none;
     margin-top: 10px;
 .attachment-container a:hover {
     background-color: black;
     color: white;
 .attachment-type {
     position: absolute;
     color: black;
     border: 2px solid black;
     background-color: white;
     margin-top: 50px;
     font-family: sans-serif;
     font-weight: 400;
     padding: 2px;
     text-transform: uppercase;
     font-size: 8px;

That's it all we need for handling file attachments. Next let's run the code.

Run the code

Webpack users can use the webpack-dev-server to build and run your app. Run the following command to bundle your application host on a local webserver:

npx webpack-dev-server --entry ./client.js --output bundle.js --debug --devtool inline-source-map


npm start

File attachment demo

Open your browser and navigate to http://localhost:8080/. Enter the meeting URL and the thread ID.

Now let's send some file attachments from Teams client like this:

A screenshot of Teams client shown a sent message with three file attachments.

Then you should see the new message being rendered along with file attachments:

A screenshot of sample app shown a received incoming message with three file attachments.

Handle image attachments

In addition to regular files, image attachment needs to be treated differently. As we wrote in the beginning, the image attachment has attachmentType of teamsImage, which requires the communication token to retrieve the preview image and full scale image.

Before we go any further, make sure you have gone through the tutorial that demonstrates how you can enable inline image support in your chat app. To summary, fetching images require a communication token in the request header. Upon getting the image blob, we need to create an ObjectUrl that points to this blob. Then we inject this URL to src attribute of each inline image.

Now you're familiar with how inline images work and it's easy to render image attachments just like a regular inline image.

Firstly, we inject an image tag to message content whenever there's an image attachment:

async function renderReceivedMessage(event) {
    messages += '<div class="container lighter">' + event.message + '</div>';
    messagesContainer.innerHTML = messages;

    // Inject image tag for all image attachments
    var imageAttachmentHtml = event.attachments
        .filter(attachment => attachment.attachmentType === "teamsImage")
        .map(attachment => renderImageAttachments(attachment))
    messagesContainer.innerHTML += imageAttachmentHtml;

    // get list of attachments and calls renderFileAttachments to construct a file attachment card
    var attachmentHtml = event.attachments
        .filter(attachment => attachment.attachmentType === "file")
        .map(attachment => renderFileAttachments(attachment))
    messagesContainer.innerHTML += attachmentHtml;

    // filter out inline images from attchments
    const imageAttachments = event.attachments.filter((attachment) =>
        attachment.attachmentType === "teamsInlineImage" ||
        attachment.attachmentType === "teamsImage");

    // fetch and render preview images

function renderImageAttachments(attachment) {
    return `<img alt="image" src="" itemscope="png" id="${attachment.id}" style="max-width: 100px">`

Now let's borrow fetchPreviewImages() from the tutorial and we should be able to use it as is without any changes:

function fetchPreviewImages(attachments) {
    if (!attachments.length > 0) {
        attachments.map(async (attachment) => {
            const response = await fetch(attachment.previewUrl, {
                method: 'GET',
                headers: {
                    'Authorization': 'Bearer ' + tokenString,
            return {
                id: attachment.id,
                content: await response.blob(),
    ).then((result) => {
        result.forEach((imageRef) => {
            const urlCreator = window.URL || window.webkitURL;
            const url = urlCreator.createObjectURL(imageRef.content);
            document.getElementById(imageRef.id).src = url;
    }).catch((e) => {
        console.log('error fetching preview images');

This function needs a tokenString so we need to have a global copy of it and initialize in init() as demonstrated in the following code snippet:

var tokenString = '';

async function init() {
    const {
    } = tokenResponse;
    tokenString = token;

That's it! Now we have added image attachment support as well. Now let's run the code and see it in action!

Image attachment demo

Now let's send some image attachments from Teams client like this:

A screenshot of Teams client shown a send box with an image attachment uploaded.

Upon sending the image attachment, you notice that it becomes an inline image on the Teams client side:

A screenshot of Teams client shown a message with the image attachment sent to the other participant.

Let's go back to our sample app, the same image should be rendered as well:

A screenshot of sample app shown an incoming message with one inline image rendered.

Next steps

For more information, see the following articles: