---
title: "Configure the Advanced I/O Function"
url: https://docs.catalyst.zoho.com/en/tutorials/alien-city/nodejs/configure-advio-function/
description: "Create a single-page web application using Catalyst Advanced I/O Function and Data Store that allows you to report or look up alien encounters in a city."
last_updated: 2026-11-04T10:10:44Z
service: All Services
type: tutorial
related_links:
  - name: "Functions"
    url: /en/serverless/help/functions/introduction/
  - name: "Advanced I/O Functions"
    url: /en/serverless/help/functions/advanced-io/
  - name: "Functions Directory Structure"
    url: /en/cli/v1/project-directory-structure/functions-directory/
---

# Configure the Advanced I/O Function

Let's begin coding the Alien City application by configuring the function component. 

The Node.js function directory ( `[ functions/alien_city_function ](https://docs.catalyst.zoho.com/en/cli/v1/project-directory-structure/functions-directory/)` ) contains the following files: 
* 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` main function file.

The two APIs in the Advanced I/O function that handle the routing between the server and the Data Store are:

* **`GET /alien`**: To check whether aliens are present in a city
* **`POST /alien`**: To report an alien presence in a city

#### Install Express Node.js Framework 

For the Node.js function, you will be using the [Express Node.js framework](https://expressjs.com/). To import the Express package in the code, you must install the Express dependencies in your system.

To install `Express.js` in your local machine, navigate to the Node function's directory (`functions/alien_city_function`) in your terminal and execute the following command:

```sh
npm install express --save
```

This will install the Express module and save the dependencies. 

![alien-city-client](https://catalyst-docs-development.zohostratus.in/images/tutorials/alcity/catalyst_alcity_install_express.webp)

This information will also be updated in the package.json file.

![alien-city-client](https://catalyst-docs-development.zohostratus.in/images/tutorials/alcity/catalyst_alcity_package_json.webp)

Let's now add the code in the function file. 

Copy the code given below and paste it in the `index.js` in the `functions/alien_city_function` 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 in this section to make sure you fully understand it. 

**index.js**

```javascript
'use strict';
var express = require('express');
var app = express();
var catalyst = require('zcatalyst-sdk-node');
app.use(express.json());
const tableName = 'AlienCity'; // The table created in the Data Store
const columnName = 'CityName'; // The column created in the table
// The POST API that reports the alien encounter for a particular city
app.post('/alien', (req, res) => {
    var cityJson = req.body;
    console.log(cityJson);
    // Initializing Catalyst SDK
    var catalystApp = catalyst.initialize(req);
    // Queries the Catalyst Data Store table and checks whether a row is present for the given city
    getDataFromCatalystDataStore(catalystApp, cityJson.city_name).then(cityDetails => {
        if (cityDetails.length == 0) { // If the row is not present, then a new row is inserted
            console.log("Alien alert!"); //Written to the logs. You can view this log from Logs under the Monitor section in the console
            var rowData = {}
            rowData[columnName] = cityJson.city_name;
            var rowArr = [];
            rowArr.push(rowData);
            // Inserts the city name as a row in the Catalyst Data Store table
            catalystApp.datastore().table(tableName).insertRows(rowArr).then(cityInsertResp => {
                res.send({
                    "message": "Thanks for reporting!"
                });
            }).catch(err => {
                console.log(err);
                sendErrorResponse(res);
            })
        } else { // If the row is present, then a message is sent indicating duplication
            res.send({
                "message": "Looks like you are not the first person to encounter aliens in this city! Someone has already reported an alien encounter here!"
            });
        }
    }).catch(err => {
        console.log(err);
        sendErrorResponse(res);
    })
});
// The GET API that checks the table for an alien encounter in that city 
app.get('/alien', (req, res) => {
    var city = req.query.city_name;
    // Initializing Catalyst SDK
    var catalystApp = catalyst.initialize(req);
    // Queries the Catalyst Data Store table and checks whether a row is present for the given city
    getDataFromCatalystDataStore(catalystApp, city).then(cityDetails => {
        if (cityDetails.length == 0) {
            res.send({
                "message": "Hurray! No alien encounters in this city yet!",
                "signal": "negative"
            });
        } else {
            res.send({
                "message": "Uh oh! Looks like there are aliens in this city!",
                "signal": "positive"
            });
        }
    }).catch(err => {
        console.log(err);
        sendErrorResponse(res);
    })
});
/**
 * Checks whether an alien encounter is already reported for the given city by querying the Data Store table
 * @param {*} catalystApp 
 * @param {*} cityName 
 */
function getDataFromCatalystDataStore(catalystApp, cityName) {
    return new Promise((resolve, reject) => {
        // Queries the Catalyst Data Store table
        catalystApp.zcql().executeZCQLQuery("SELECT * FROM AlienCity WHERE CityName = '" + cityName + "'").then(queryResponse => {
            resolve(queryResponse);
        }).catch(err => {
            reject(err);
        })
    });
}
/**
 * Sends an error response
 * @param {*} res 
 */
function sendErrorResponse(res) {
    res.status(500);
    res.send({
        "error": "Internal server error occurred. Please try again in some time."
    });
}
module.exports = app;

```

The functions directory is now configured. We will discuss the architecture of the function and the client in the next section.