Creating an interactive modal

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A modal is similar to an alert box, pop-up, or dialog box within Slack. Modals capture and maintain focus within Slack until the user submits or closes the modal. This makes them a powerful piece of app functionality for engaging with users.

Interactive modals are modals containing interactive Block Kit elements. Modals have a larger catalog of available interactive Block Kit elements than messages.

Modals can be opened via a Block Kit interaction or a trigger. A modal is updated by View events (close and submit) to reflect the user's inputs as they interact with the modal.

This guide will use the an example file from our deno-code-snippets repository.

If you'd like a full sample app that uses modal interactivity, check out the Simple Survey sample app.

1. Add interactivity to your function definition

A function needs to have the interactivity input parameter added to have interactive functionality. The interactivity parameter is required to ensure users don't experience any unexpected or unwanted modals appearing—only their interaction can open a modal.

For modals, interactivity takes the form of the unique identifier interactivityPointer. A property with the type Schema.slack.types.interactivity is added to the properties object within a function's input_parameters. Your function can then access that interactivity event via inputs.interactivity.interactivity_pointer.

In our example file /Block_Kit_Modals/functions/demo.ts, interactivityis added to the function's input parameters:

// /functions.demo.ts

import { DefineFunction, Schema, SlackFunction } from "deno-slack-sdk/mod.ts";

export const def = DefineFunction({
  callback_id: "block-kit-modal-demo",
  title: "Block Kit modal demo",
  source_file: "Block_Kit_Modals/functions/demo.ts",
  input_parameters: {
    properties: { interactivity: { type: Schema.slack.types.interactivity } },
    required: ["interactivity"],
  },
  output_parameters: { properties: {}, required: [] },
});
// To be continued ...

2. Build a modal view

Modal views are constructed partially using Block Kit pieces. That view will then be placed within an API call later on.

Below is our example modal:

view: {
  "type": "modal",
  // Note that this ID can be used for dispatching view submissions and view closed events.
  "callback_id": "first-page",
  // This option is required to be notified when this modal is closed by the user
  "notify_on_close": true,
  "title": { "type": "plain_text", "text": "My App" },
  // Not all modals need a submit button, but since we want to collect input, we do
  "submit": { "type": "plain_text", "text": "Next" },
  "close": { "type": "plain_text", "text": "Close" },
  "blocks": [
    {
      "type": "input",
      "block_id": "first_text",
      "element": { "type": "plain_text_input", "action_id": "action" },
      "label": { "type": "plain_text", "text": "First" },
    },
  ],
},

3. Open the modal within your function

With interactivity added to the function definition, we can open the interactive modal view. A view is opened using the views.open method.

A modal view can be opened based on either of the following, causing your function run:

  • a trigger (for example, clicking on a link trigger)
  • a previous Block Kit action (for example, clicking a button in a message)

Our example uses the first method.

Some important considerations to note so that you can ensure your modal isn't left floating in the vast sea of suspended modals:

  1. Take note of the callback_id. We'll use it to define modal view handlers that react to view open/closed events later.
  2. Set notify_on_close to true in order to trigger a view_closed event.

Opening a modal based on a trigger

View this example in demo.ts:

// demo.ts

export default SlackFunction(
  def,
  // ---------------------------
  // The first handler function that opens a modal.
  // This function can be called when the workflow executes the function step.
  // ---------------------------
  async ({ inputs, client }) => {
    // Open a new modal with the end-user who interacted with the link trigger
    const response = await client.views.open({
      interactivity_pointer: inputs.interactivity.interactivity_pointer,
      view: {
        "type": "modal",
        // Note that this ID can be used for dispatching view submissions and view closed events.
        "callback_id": "first-page",
        // This option is required to be notified when this modal is closed by the user
        "notify_on_close": true,
        "title": { "type": "plain_text", "text": "My App" },
        "submit": { "type": "plain_text", "text": "Next" },
        "close": { "type": "plain_text", "text": "Close" },
        "blocks": [
          {
            "type": "input",
            "block_id": "first_text",
            "element": { "type": "plain_text_input", "action_id": "action" },
            "label": { "type": "plain_text", "text": "First" },
          },
        ],
      },
    });
    if (response.error) {
      const error =
        `Failed to open a modal in the demo workflow. Contact the app maintainers with the following information - (error: ${response.error})`;
      return { error };
    }
    return {
      // To continue with this interaction, return false for the completion
      completed: false,
    };
  },
)

Make sure to set the return to completed: false. You'll then set it to true later in your modal view event handler.

Opening a modal based on a Block Kit action

Alternatively, a modal view can be opened using a Block Kit action handler. Below is the code structure for doing so:

export default SlackFunction(ConfigureEventsFunctionDefinition, async ({ inputs, client }) => {

// "function_name" is the action_id of the Block element from which the action originated
).addBlockActionsHandler(["function_name"], async ({ body, client }) => {
  const openingModal = await client.views.open({
    interactivity_pointer: body.interactivity.interactivity_pointer,
    view,
  });
  if (openingModal.error) {
    const error = `Failed to open a modal - ${openingModal.error}`;
    return { error };
  }
});

4. Update the modal view (optional)

With your defined modal view equipped with a callback_id, you can implement a modal view event handler to respond to interactions with your modal view. To respond to a submitted view, the action of the user clicking the 'submit' button in your modal, use addViewSubmissionHandler.

The handler can update or push a view in two ways:

In the examples below, the addViewSubmissionHandler method registers a handler to push a new view on to the view stack.

The first code snippet shows how to push a new view by calling views.push:

// ...
.addViewSubmissionHandler(
  "first-page", // The callback_id of the modal
  async ({ inputs, client, body }) => {
    const response = await client.views.push({
      interactivity_pointer: inputs.interactivity.interactivity_pointer,
      view, 
    });
  },
)
// ...

The second code snippet shows how to use response_action to do the same thing. Both result in identical behavior!

// ...
.addViewSubmissionHandler(
  "first-page", // The callback_id of the modal
  async () => {
    return {
      response_action: "push",
      view, 
    };
  },
)
// ...

In our example, we'll be using the second way—updating response_action—to provide a second modal view when the first modal data is submitted.

Example: updating with a new interactive modal

In this example, notice how we extract the input values from the prior view using view.state.values. This is a property of the view interaction payload.

  // ---------------------------
  // The handler that can be called when the above modal data is submitted.
  // It saves the inputs from the first page as private_metadata,
  // and then displays the second-page modal view.
  // ---------------------------
  .addViewSubmissionHandler(["first-page"], ({ view }) => {
    // Extract the input values from the view data
    const firstText = view.state.values.first_text.action.value;
    // Input validations
    if (firstText.length < 20) {
      return {
        response_action: "errors",
        // The key must be a valid block_id in the blocks on a modal
        errors: { first_text: "Must be 20 characters or longer" },
      };
    }
    // Successful. Update the modal with the second page presentation
    return {
      response_action: "update",
      view: {
        "type": "modal",
        "callback_id": "second-page",
        // This option is required to be notified when this modal is closed by the user
        "notify_on_close": true,
        "title": { "type": "plain_text", "text": "My App" },
        "submit": { "type": "plain_text", "text": "Next" },
        "close": { "type": "plain_text", "text": "Close" },
        // Hidden string data, which is not visible to end-users
        // You can use this property to transfer the state of interaction
        // to the following event handlers.
        // (Up to 3,000 characters allowed)
        "private_metadata": JSON.stringify({ firstText }),
        "blocks": [
          // Display the inputs from "first-page" modal view
          {
            "type": "section",
            "text": { "type": "mrkdwn", "text": `First: ${firstText}` },
          },
          // New input block to receive text
          {
            "type": "input",
            "block_id": "second_text",
            "element": { "type": "plain_text_input", "action_id": "action" },
            "label": { "type": "plain_text", "text": "Second" },
          },
        ],
      },
    };
  })

Example: updating with a static confirmation modal

  // ---------------------------
  // The handler that can be called when the second modal data is submitted.
  // It displays the completion page view with the inputs from
  // the first and second pages.
  // ---------------------------
  .addViewSubmissionHandler(["second-page"], ({ view }) => {
    // Extract the first-page inputs from private_metadata
    const { firstText } = JSON.parse(view.private_metadata!);
    // Extract the second-page inputs from the view data
    const secondText = view.state.values.second_text.action.value;
    // Displays the third page, which tells the completion of the interaction
    return {
      response_action: "update",
      view: {
        "type": "modal",
        "callback_id": "completion",
        // This option is required to be notified when this modal is closed by the user
        "notify_on_close": true,
        "title": { "type": "plain_text", "text": "My App" },
        // This modal no longer accepts further inputs.
        // So, the "Submit" button is intentionally removed from the view.
        "close": { "type": "plain_text", "text": "Close" },
        // Display the two inputs
        "blocks": [
          {
            "type": "section",
            "text": { "type": "mrkdwn", "text": `First: ${firstText}` },
          },
          {
            "type": "section",
            "text": { "type": "mrkdwn", "text": `Second: ${secondText}` },
          },
        ],
      },
    };
  })

5. Close the modal

To respond to a closed view, the action of the user clicking the 'close' button on your modal, use addViewClosedHandler.

  // ---------------------------
  // The handler that can be called when the second modal data is closed.
  // If your app runs some resource-intensive operations on the backend side,
  // you can cancel the ongoing process and/or tell the end-user
  // what to do next in DM and so on.
  // ---------------------------
  .addViewClosedHandler(
    ["first-page", "second-page", "completion"],
    ({ view }) => {
      console.log(`view_closed handler called: ${JSON.stringify(view)}`);
      return { completed: true };
    },
  );

You can also add a call to the private client.functions.completeSuccess method to explicitly mark the function as complete like this:

const response = await client.functions.completeSuccess({
  function_execution_id: body.function_data.execution_id,
  outputs,
});

Handling errors

The errors in the above examples were handled like so:

if (response.error) {
  const error =
    `Failed to open a modal in the demo workflow. Contact the app maintainers with the following information - (error: ${response.error})`;
  return { error };
    }

If the function execution was not successful, you can also add a call to the private client.functions.completeError method to raise an error like so:

const response = await client.functions.completeError({
  function_execution_id: body.function_data.execution_id,
  error: "Error completing function",
});

Once you have opened a modal and handled your modal views, you may decide that you'd like to display any potential data validation error messages to your users. It is important to validate the inputs you receive from the user: first, that the user is authorized to pass the input, and second, that the user is passing a value you expect to receive and nothing more.

As long as your submission handler returns an error object defined on this page, the error messages you include in that object will be displayed right next to the relevant form fields based on their field IDs.

Onward

You now have some shiny new modal views weaved within your app, and are on a course to providing a wonderful user experience.

To learn more about other interactivity options, refer to the Interactivity overview.


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