Build a Google Workspace add-on with Apps Script

This quickstart creates a simple Google Workspace add-on that demonstrates homepages, contextual triggers, and connecting to third-party APIs.

The add-on creates contextual and non-contextual interfaces in Gmail, Calendar, and Drive. The add-on displays a random image of a cat with text overlaying the image. The text is either static for homepages or taken from the host application context for contextual triggers.

Objectives

  • Set up your environment.
  • Set up the script.
  • Run the script.

Prerequisites

To use this sample, you need the following prerequisites:

  • A Google Account (Google Workspace accounts might require administrator approval).

  • A web browser with access to the internet.

  • A Google Cloud project.

Set up your environment

Open your Cloud project in the Google Cloud console

If it's not open already, open the Cloud project that you intend to use for this sample:

  1. In the Google Cloud console, go to the Select a project page.

    Select a Cloud project

  2. Select the Google Cloud project you want to use. Or, click Create project and follow the on-screen instructions. If you create a Google Cloud project, you might need to turn on billing for the project.

Google Workspace add-ons require a consent screen configuration. Configuring your add-on's OAuth consent screen defines what Google displays to users.

  1. In the Google Cloud console, go to Menu > APIs & Services > OAuth consent screen.

    Go to OAuth consent screen

  2. For User type select Internal, then click Create.
  3. Complete the app registration form, then click Save and Continue.

  4. For now, you can skip adding scopes and click Save and Continue. In the future, when you create an app for use outside of your Google Workspace organization, you must change the User type to External, and then, add the authorization scopes that your app requires.

  5. Review your app registration summary. To make changes, click Edit. If the app registration looks OK, click Back to Dashboard.

Set up the script

Create the Apps Script project

  1. To create a new Apps Script project, go to script.new.
  2. Click Untitled project.
  3. Rename the Apps Script project Cats and click Rename.
  4. Next to the Code.gs file, click More > Rename. Name the file Common.
  5. Click Add a file > Script. Name the file Gmail.
  6. Repeat step 5 to create 2 more script files named Calendar and Drive. When you're done you should have 4 separate script files.

  7. Replace the contents of each file with the following corresponding code:

    Common.gs

      /**
 * This simple Google Workspace Add-on shows a random image of a cat in the
 * sidebar. When opened manually (the homepage card), some static text is
 * overlayed on the image, but when contextual cards are opened a new cat image
 * is shown with the text taken from that context (such as a message's subject
 * line) overlaying the image. There is also a button that updates the card with
 * a new random cat image.
 *
 * Click "File > Make a copy..." to copy the script, and "Publish > Deploy from
 * manifest > Install add-on" to install it.
 */

/**
 * The maximum number of characters that can fit in the cat image.
 */
var MAX_MESSAGE_LENGTH = 40;

/**
 * Callback for rendering the homepage card.
 * @return {CardService.Card} The card to show to the user.
 */
function onHomepage(e) {
  console.log(e);
  var hour = Number(Utilities.formatDate(new Date(), e.userTimezone.id, 'H'));
  var message;
  if (hour >= 6 && hour < 12) {
    message = 'Good morning';
  } else if (hour >= 12 && hour < 18) {
    message = 'Good afternoon';
  } else {
    message = 'Good night';
  }
  message += ' ' + e.hostApp;
  return createCatCard(message, true);
}

/**
 * Creates a card with an image of a cat, overlayed with the text.
 * @param {String} text The text to overlay on the image.
 * @param {Boolean} isHomepage True if the card created here is a homepage;
 *      false otherwise. Defaults to false.
 * @return {CardService.Card} The assembled card.
 */
function createCatCard(text, isHomepage) {
  // Explicitly set the value of isHomepage as false if null or undefined.
  if (!isHomepage) {
    isHomepage = false;
  }

  // Use the "Cat as a service" API to get the cat image. Add a "time" URL
  // parameter to act as a cache buster.
  var now = new Date();
  // Replace forward slashes in the text, as they break the CataaS API.
  var caption = text.replace(/\//g, ' ');
  var imageUrl =
      Utilities.formatString('https://cataas.com/cat/says/%s?time=%s',
          encodeURIComponent(caption), now.getTime());
  var image = CardService.newImage()
      .setImageUrl(imageUrl)
      .setAltText('Meow')

  // Create a button that changes the cat image when pressed.
  // Note: Action parameter keys and values must be strings.
  var action = CardService.newAction()
      .setFunctionName('onChangeCat')
      .setParameters({text: text, isHomepage: isHomepage.toString()});
  var button = CardService.newTextButton()
      .setText('Change cat')
      .setOnClickAction(action)
      .setTextButtonStyle(CardService.TextButtonStyle.FILLED);
  var buttonSet = CardService.newButtonSet()
      .addButton(button);

  // Create a footer to be shown at the bottom.
  var footer = CardService.newFixedFooter()
      .setPrimaryButton(CardService.newTextButton()
          .setText('Powered by cataas.com')
          .setOpenLink(CardService.newOpenLink()
              .setUrl('https://cataas.com')));

  // Assemble the widgets and return the card.
  var section = CardService.newCardSection()
      .addWidget(image)
      .addWidget(buttonSet);
  var card = CardService.newCardBuilder()
      .addSection(section)
      .setFixedFooter(footer);

  if (!isHomepage) {
    // Create the header shown when the card is minimized,
    // but only when this card is a contextual card. Peek headers
    // are never used by non-contexual cards like homepages.
    var peekHeader = CardService.newCardHeader()
      .setTitle('Contextual Cat')
      .setImageUrl('https://www.gstatic.com/images/icons/material/system/1x/pets_black_48dp.png')
      .setSubtitle(text);
    card.setPeekCardHeader(peekHeader)
  }

  return card.build();
}

/**
 * Callback for the "Change cat" button.
 * @param {Object} e The event object, documented {@link
 *     https://developers.google.com/gmail/add-ons/concepts/actions#action_event_objects
 *     here}.
 * @return {CardService.ActionResponse} The action response to apply.
 */
function onChangeCat(e) {
  console.log(e);
  // Get the text that was shown in the current cat image. This was passed as a
  // parameter on the Action set for the button.
  var text = e.parameters.text;

  // The isHomepage parameter is passed as a string, so convert to a Boolean.
  var isHomepage = e.parameters.isHomepage === 'true';

  // Create a new card with the same text.
  var card = createCatCard(text, isHomepage);

  // Create an action response that instructs the add-on to replace
  // the current card with the new one.
  var navigation = CardService.newNavigation()
      .updateCard(card);
  var actionResponse = CardService.newActionResponseBuilder()
      .setNavigation(navigation);
  return actionResponse.build();
}

/**
 * Truncate a message to fit in the cat image.
 * @param {string} message The message to truncate.
 * @return {string} The truncated message.
 */
function truncate(message) {
  if (message.length > MAX_MESSAGE_LENGTH) {
    message = message.slice(0, MAX_MESSAGE_LENGTH);
    message = message.slice(0, message.lastIndexOf(' ')) + '...';
  }
  return message;
}

    Gmail.gs

      /**
 * Callback for rendering the card for a specific Gmail message.
 * @param {Object} e The event object.
 * @return {CardService.Card} The card to show to the user.
 */
function onGmailMessage(e) {
  console.log(e);
  // Get the ID of the message the user has open.
  var messageId = e.gmail.messageId;

  // Get an access token scoped to the current message and use it for GmailApp
  // calls.
  var accessToken = e.gmail.accessToken;
  GmailApp.setCurrentMessageAccessToken(accessToken);

  // Get the subject of the email.
  var message = GmailApp.getMessageById(messageId);
  var subject = message.getThread().getFirstMessageSubject();

  // Remove labels and prefixes.
  subject = subject
      .replace(/^([rR][eE]|[fF][wW][dD])\:\s*/, '')
      .replace(/^\[.*?\]\s*/, '');

  // If neccessary, truncate the subject to fit in the image.
  subject = truncate(subject);

  return createCatCard(subject);
}

/**
 * Callback for rendering the card for the compose action dialog.
 * @param {Object} e The event object.
 * @return {CardService.Card} The card to show to the user.
 */
function onGmailCompose(e) {
  console.log(e);
  var header = CardService.newCardHeader()
      .setTitle('Insert cat')
      .setSubtitle('Add a custom cat image to your email message.');
  // Create text input for entering the cat's message.
  var input = CardService.newTextInput()
      .setFieldName('text')
      .setTitle('Caption')
      .setHint('What do you want the cat to say?');
  // Create a button that inserts the cat image when pressed.
  var action = CardService.newAction()
      .setFunctionName('onGmailInsertCat');
  var button = CardService.newTextButton()
      .setText('Insert cat')
      .setOnClickAction(action)
      .setTextButtonStyle(CardService.TextButtonStyle.FILLED);
  var buttonSet = CardService.newButtonSet()
      .addButton(button);
  // Assemble the widgets and return the card.
  var section = CardService.newCardSection()
      .addWidget(input)
      .addWidget(buttonSet);
  var card = CardService.newCardBuilder()
      .setHeader(header)
      .addSection(section);
  return card.build();
}

/**
 * Callback for inserting a cat into the Gmail draft.
 * @param {Object} e The event object.
 * @return {CardService.UpdateDraftActionResponse} The draft update response.
 */
function onGmailInsertCat(e) {
  console.log(e);
  // Get the text that was entered by the user.
  var text = e.formInput.text;
  // Use the "Cat as a service" API to get the cat image. Add a "time" URL
  // parameter to act as a cache buster.
  var now = new Date();
  var imageUrl = 'https://cataas.com/cat';
  if (text) {
    // Replace forward slashes in the text, as they break the CataaS API.
    var caption = text.replace(/\//g, ' ');
    imageUrl += Utilities.formatString('/says/%s?time=%s',
        encodeURIComponent(caption), now.getTime());
  }
  var imageHtmlContent = '<img style="display: block; max-height: 300px;" src="'
      + imageUrl + '"/>';
  var response = CardService.newUpdateDraftActionResponseBuilder()
      .setUpdateDraftBodyAction(CardService.newUpdateDraftBodyAction()
          .addUpdateContent(imageHtmlContent,CardService.ContentType.MUTABLE_HTML)
          .setUpdateType(CardService.UpdateDraftBodyType.IN_PLACE_INSERT))
      .build();
  return response;
}

    Calendar.gs

      /**
 * Callback for rendering the card for a specific Calendar event.
 * @param {Object} e The event object.
 * @return {CardService.Card} The card to show to the user.
 */
function onCalendarEventOpen(e) {
  console.log(e);
  var calendar = CalendarApp.getCalendarById(e.calendar.calendarId);
  // The event metadata doesn't include the event's title, so using the
  // calendar.readonly scope and fetching the event by it's ID.
  var event = calendar.getEventById(e.calendar.id);
  if (!event) {
    // This is a new event still being created.
    return createCatCard('A new event! Am I invited?');
  }
  var title = event.getTitle();
  // If necessary, truncate the title to fit in the image.
  title = truncate(title);
  return createCatCard(title);
}

    Drive.gs

      /**
 * Callback for rendering the card for specific Drive items.
 * @param {Object} e The event object.
 * @return {CardService.Card} The card to show to the user.
 */
function onDriveItemsSelected(e) {
  console.log(e);
  var items = e.drive.selectedItems;
  // Include at most 5 items in the text.
  items = items.slice(0, 5);
  var text = items.map(function(item) {
    var title = item.title;
    // If neccessary, truncate the title to fit in the image.
    title = truncate(title);
    return title;
  }).join('\n');
  return createCatCard(text);
}

  8. Click Project Settings The icon for project settings.

  9. Check the Show "appsscript.json" manifest file in editor box.

  10. Click Editor .

  11. Open the appsscript.json file and replace the contents with the following code, then click Save Save icon.

    appsscript.json

       {
  "timeZone": "America/New_York",
  "dependencies": {
  },
  "exceptionLogging": "STACKDRIVER",
  "oauthScopes": [
    "https://www.googleapis.com/auth/calendar.addons.execute",
    "https://www.googleapis.com/auth/calendar.readonly",
    "https://www.googleapis.com/auth/drive.addons.metadata.readonly",
    "https://www.googleapis.com/auth/gmail.addons.current.action.compose",
    "https://www.googleapis.com/auth/gmail.addons.current.message.readonly",
    "https://www.googleapis.com/auth/gmail.addons.execute",
    "https://www.googleapis.com/auth/script.locale"],
  "runtimeVersion": "V8",
  "addOns": {
    "common": {
      "name": "Cats",
      "logoUrl": "https://www.gstatic.com/images/icons/material/system/1x/pets_black_48dp.png",
      "useLocaleFromApp": true,
      "homepageTrigger": {
        "runFunction": "onHomepage",
        "enabled": true
      },
      "universalActions": [{
        "label": "Learn more about Cataas",
        "openLink": "https://cataas.com"
      }]
    },
    "gmail": {
      "contextualTriggers": [{
        "unconditional": {
        },
        "onTriggerFunction": "onGmailMessage"
      }],
      "composeTrigger": {
        "selectActions": [{
          "text": "Insert cat",
          "runFunction": "onGmailCompose"
        }],
        "draftAccess": "NONE"
      }
    },
    "drive": {
      "onItemsSelectedTrigger": {
        "runFunction": "onDriveItemsSelected"
      }
    },
    "calendar": {
      "eventOpenTrigger": {
        "runFunction": "onCalendarEventOpen"
      }
    }
  }
}

Copy the Cloud project number

  1. In the Google Cloud console, go to Menu > IAM & Admin > Settings.

    Go to IAM & Admin Settings

  2. In the Project number field, copy the value.

Set the Apps Script project's Cloud project

  1. In your Apps Script project, click Project Settings The icon for project settings.
  2. Under Google Cloud Platform (GCP) Project, click Change project.
  3. In GCP project number, paste the Google Cloud project number.
  4. Click Set project.

Install a test deployment

  1. In your Apps Script project, click Editor .
  2. Click Deploy > Test deployments.
  3. Click Install > Done.

Run the script

  1. Go to Gmail.
  2. To open the add-on, in the right side panel, click Cats .
  3. If prompted, authorize the add-on.
  4. The add-on displays a cat image and text. To change the image, click Change cat.
  5. If you open an email while the add-on is open, the image refreshes and the text changes to the subject line of the email (truncated if it's too long).

You can see similar functionality in Calendar and Drive. You don't need to reauthorize the add-on to use it in those host apps.

Next steps