---
title: "Code Your Event Function"
url: https://docs.catalyst.zoho.com/en/tutorials/event-app/nodejs/configure-function/
description: "Configure a Catalyst Event Function and associate it with a Rule in Catalyst Signals that will send automated onboarding emails to the application users when they sign up."
last_updated: 2026-08-17T12:16:04Z
service: All Services
type: tutorial
related_links:
  - name: "Event Functions"
    url: /en/serverless/help/functions/event-functions/
  - name: "Functions Directory Structure"
    url: /en/cli/v1/project-directory-structure/functions-directory
  - name: "Web Client Hosting"
    url: /en/cloud-scale/help/web-client-hosting/introduction/
---

# Code Your Event Function

Let's now configure the Event function, `event_app`, that will send automated onboarding emails to the user with a link to a form. This form enables the user to provide their personal details to register for the client application. This function will be executed when the event listener triggers it.

The [functions directory](https://docs.catalyst.zoho.com/en/cli/v1/project-directory-structure/functions-directory), `functions/event_app` contains:

* The `index.js` main function file
* The `catalyst-config.json` configuration file
* Node modules
* `[package.json](https://docs.npmjs.com/files/package.json)` and `[package-lock.json](https://docs.npmjs.com/configuring-npm/package-lock-json.html)` dependency files

You will be adding code in the `index.js` file.

Copy the Node.js code and paste it in `index.js` in the `functions/event_app` directory of your project, and save the file. You can use any IDE of your choice to work with the application's files.

> **Note**: Please go through the code given in this section to ensure you fully understand it. 

**index.js**

```javascript
const catalyst = require("zcatalyst-sdk-node");
const fs = require("fs");
const path = require("path");
module.exports = (event, context) => {
  try {
    const app = catalyst.initialize(context);
    let eventData = event.getRawData();
    let userEmailId = eventData.email;
    let email = app.email();
    let config = {
      from_email: "emmy@zylker.com", // Replace this with the email you configured
      to_email: userEmailId,
      subject: "We welcome you on board!",
      content: fs.readFileSync(path.join(__dirname, "invite.html")).toString(),
      html_mode: true,
    };
    let mailPromise = email.sendMail(config);
    mailPromise.then((mailObject) => {
      console.log(mailObject);
      context.closeWithSuccess();
    });
  } catch (err) {
    console.error(err);
    context.closeWithFailure();
  }
};

```

> **Note:** Replace the value of `from_email` in **line 11** with the email address that you configured for your application through Catalyst Mail previously.

### Deploy Your Project

You need to deploy your project to the Catalyst console to ensure the event function and the application URL are available to use while configuring the [Rule](https://docs.catalyst.zoho.com/en/signals/help/rules/key-aspects/).

> **Note:** We will be deploying the entire project to the Catalyst console one more time once we configure the client for your application and complete testing the application.

To [deploy the project to the console](https://docs.catalyst.zoho.com/en/cli/v1/deploy-resources/introduction/), enter the following command in your CLI and execute it.

```sh
catalyst deploy
```

![catalyst_tutorials_eventapp_cli__first_deploy](https://catalyst-docs-development.zohostratus.in/images/tutorials/event-app/catalyst_tutorials_eventapp_cli__first_deploy.webp)

The project has been deployed to the console.

You can copy the application URL from the CLI, or you can copy it from the [Web Client Hosting](https://docs.catalyst.zoho.com/en/cloud-scale/help/web-client-hosting/introduction/) component.

![catalyst_tutorials_eventapp_web_cli_first_deploy](https://catalyst-docs-development.zohostratus.in/images/tutorials/event-app/catalyst_tutorials_eventapp_web_cli_first_deploy.webp)

> **Note:** We will learn more about deploying your application to the console and to production when we reach **Step 6** of the tutorial. You can also learn more about deploying catalyst resources to the console form this [help documentation](https://docs.catalyst.zoho.com/en/cli/v1/deploy-resources/introduction/).

### Configure Your Product Tour

Now, create a html file in the `functions/event_app` directory and name it `invite.html`.

The `invite.html` page will contain the product tour.

Copy the following code and paste it in the `invite.html` file.

**invite.html**

```xml
<div class="mT" style="background-color: #f2f2f2;padding: 4%;">
    <div style="width: 100%;max-width: 750px; margin: 0px auto;padding-bottom:10px;">
        <img src="" alt="">
    </div>
    <div
        style="width: 100%;max-width: 750px;font-size: 16px; margin: 0 auto;background: #fff; font-family: lucida grande,lucida sans,lucida sans unicode,arial,helvetica,verdana,sans-serif;">
        <table style="display: table;width: 100%;" cellspacing="0" cellpadding="0">
            <tr>
                <td style="background-color: #e80f28;height: 2px;width:25%;"> </td>
                <td style="background-color: #e80f28;height: 2px;width:25%;"> </td>
                <td style="background-color: #e80f28;height: 2px;width:25%;"> </td>
                <td style="background-color: #e80f28;height: 2px;width:25%;"> </td>
            </tr>
        </table>
        <div style="padding: 8% 5%;border: 1px solid #f3f3f3;line-height: 1.625em;">
            <div style="font-size: 0.8125em;color: #3c3c3c;">Hey there!</div>
            <br />
            <div style="font-size: 0.8125em;color:#5d5d5d; line-height: 1.625em;padding-bottom: 20px;">
            </div>
            Welcome to Event App! We have a range of interesting and innovative features for you to explore. Please take the time to read through our product tour document.
            <div style="font-size: 0.8125em;color: #5d5d5d;line-height: 1.625em;padding-bottom: 20px;">
            <a href="https://eventapp-779513891.development.catalystserverless.com/app/tour.html">Take the tour!</a> <!-- Replace here -->
            </div>
            <div style="font-size: 0.8125em;color: #5d5d5d;line-height: 1.625em;padding-bottom: 20px;">
                If the link doesn't work, please copy the following address and paste it in your browser.
            </div>
            <div style="font-size: 0.8125em; line-height: 1.625em; width: 100%; padding:10px 0px; background-color: rgb(241,241,241);border: rgb(253,253,253) solid 1.0px;margin: 0.0px auto;">
                <div style="margin: 0.0px 10.0px;color: rgb(0,0,255);">
                 <a href="https://eventapp-779513891.development.catalystserverless.com/app/tour.html"> https://eventapp-779513891.development.catalystserverless.com/app/tour.html</a> <!-- Replace here -->
                </div>
            </div>
            <br />
            <div style="font-size: 0.8125em;color: #5d5d5d;line-height: 1.625em;">
                <div>Regards,</div>
                <div>EventApp Team</div>
            </div>
        </div>
    </div>
</div>

```

> **Note:** Replace "**https:<span>//eventapp-779513891.development.catalystserverless.com**" in the code with the Project Domain Name you generated for your project in **lines 22 and 29**.

The Event function is now configured.