---
title: "Configure the Basic I/O function"
url: https://docs.catalyst.zoho.com/en/tutorials/microservice/nodejs/configure-function/
description: "Build a microservice using Catalyst Basic I/O Functions and Zoho CRM to send email alerts when more than a specific number of leads are created."
last_updated: 2026-11-04T10:10:44Z
service: All Services
type: tutorial
related_links:
  - name: "Functions"
    url: /en/serverless/help/functions/introduction/
  - name: "Functions Directory"
    url: /en/cli/v1/project-directory-structure/functions-directory/
---

# Configure the Function

Let's begin coding the microservice.
The [functions directory](https://docs.catalyst.zoho.com/en/cli/v1/project-directory-structure/functions-directory), in this case `functions/counter_based_alert_function`, 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.

We will be adding code in the `index.js` file. You can use any IDE of your choice to configure the function.

> **Note:** Please go through the code given in this section for understanding it better.

Copy the code given below and paste it in `index.js` and save the file.

**index.js**

```javascript
const catalyst = require("zcatalyst-sdk-node");
module.exports = async(context, basicIO) => {
try {
 const FROM_EMAIL="emma@zylker.com"; // The email address of the sender. Replace this with the email address you configured in Mail.
 const TO_EMAIL="brandon.cooper@zylker.com"; // Replace this with the email address that you want the alert email to be sent to. 
 let featureName = basicIO.getArgument("feature_name");
 let mailCountThreshold = basicIO.getArgument("mail_count_threshold");
 let app =  catalyst.initialize(context);
 let value = null;
 let cache = app.cache();
 let segment = cache.segment();
 let cachePromise = segment.getValue("COUNTER_" + featureName);
 await cachePromise.then((entity) => {
     value = entity;			
 	}).catch((err) => {
 		throw err;				
 		});
  if (value == null) {
         await segment.put("COUNTER_" + featureName,1,1);
    } else {
 	let count = parseInt(value);	
 	// If the value is not null, then the count is incremented by 1.
 	count++;	
 	// Writes the count value to the default segment of Catalyst cache	
 	await segment.put("COUNTER_" + featureName,count,1);	
 	// If the current count is greater than the threshold value, then an email alert is sent to the receiver configured above
 	if (count > parseInt(mailCountThreshold)) {
 		//Create a config object with the email configuration
 		let config = {
 			from_email: FROM_EMAIL, 
 			to_email: [TO_EMAIL],				
 			subject: 'Alert!',
 			content: "Count exceeded the threshold limit for the feature:" +featureName,				
 		};
 		//Send the mail by passing the config object
 		let email = app.email();
 		let mailPromise = email.sendMail(config);
 		await mailPromise.then((mailObject) => {	
 				console.log("Email Alert Sent");						
 			})
 			.catch((err) => {
 			throw err;				
 			});		
 	}
    }
    // Handles the 200 status code
 	 basicIO.setStatus(200);
 	 basicIO.write("The function executed successfully");
 } catch (error) {
 	console.log("Exception occurred while processing",error.toString()); //Written to the logs. You can view this log from Logs under the Monitor section in the console
 	// Handles the 500 status code, when an exception occurs
 	basicIO.setStatus(500);
 	basicIO.write("Error in the function execution");
 	}
 context.close(); //end of application
};

```

> **Note**: Before you proceed to the next step, ensure that you replace the values of `FROM_EMAIL` in line **5** and `TO_EMAIL` in line **6** in the code as directed.

### Working of the Basic I/O function

As discussed in the Introduction, the function obtains the inputs for `feature_name` and `mail_count_threshold` from the user through the API, when it is invoked. It obtains the current counter value from the cache and then increments it by 1 after every invocation. It then writes the new counter value to the cache. 

> **Note**: Because we are using the default segment in Catalyst Cache, we need not configure it or create a new segment. You can learn more about this from the [Cache help page](https://docs.catalyst.zoho.com/en/cloud-scale/help/cache/introduction)

If the current counter value is greater than the threshold limit specified by the user, the email alert will be sent to the address defined in the code. This information is also pushed to [Catalyst Logs](https://docs.catalyst.zoho.com/en/devops/help/logs/introduction) with an appropriate message. You can check this from *Logs* under the *Monitor* section in the Catalyst console.

The functions directory is now configured.