Polling Requests to an API in JavaScript
Tags: javascript, react, api, reactnative
Published: 2024-06-17 20:26:19

Polling is a technique that repeatedly requests data from a server at regular intervals until a desired response is received or a timeout period elapses. In this article, we will explore how to implement a polling request method in JavaScript to repeatedly hit an API every 5 seconds for up to 300 seconds (5 minutes) or until a successful response is received.


## Understanding Polling

Polling involves sending periodic requests to an API to check for an update or a specific response. This can be particularly useful in scenarios where you need to wait for a process to complete on the server and then perform actions based on the result.

## Polling Logic

Here is a step-by-step breakdown of the polling logic we will implement:

1. Define the API endpoint and desired success response.
2. Set the polling interval (5 seconds) and maximum polling duration (300 seconds).
3. Use a loop or a recursive function to repeatedly send requests to the API at the specified interval.
4. Check the API response after each request.
5. Stop polling if a successful response is received or the maximum polling duration is reached.

## Implementing Polling in JavaScript

Let's implement this logic in JavaScript:

Step 1: Define the API Endpoint and Success Response

```
const apiEndpoint = 'https://example.com/api/endpoint'; // Replace with your API endpoint
const successResponse = 'success'; // Define what constitutes a success response

```

Step 2: Set Polling Interval and Maximum Duration

```
const pollingInterval = 5000; // 5 seconds in milliseconds
const maxPollingDuration = 300000; // 300 seconds (5 minutes) in milliseconds

```
Step 3: Implement the Polling Function

We will create a function pollApi that handles the polling logic. This function will use setTimeout to schedule the next API request if necessary.

```
async function pollApi(apiEndpoint, successResponse, pollingInterval, maxPollingDuration) {
    const startTime = Date.now(); // Record the start time

    const makeRequest = async () => {
        try {
            const response = await fetch(apiEndpoint); // Make request
            const data = await response.json();

            if (data.status === successResponse) {
                console.log('Success response received:', data);
                return; // // Stop polling if success response
            }

            const elapsedTime = Date.now() - startTime;

            if (elapsedTime < maxPollingDuration) {
                setTimeout(makeRequest, pollingInterval); // Schedule next request
            } else {
                console.log('Maximum polling duration reached. Stopping polling.');
            }
        } catch (error) {
            console.error('Error making API request:', error);
            const elapsedTime = Date.now() - startTime;

            if (elapsedTime < maxPollingDuration) {
                setTimeout(makeRequest, pollingInterval); // Schedule next request
            } else {
                console.log('Maximum polling duration reached. Stopping polling.');
            }
        }
    };

    makeRequest(); // Start the first request
}

```

Step 4: Start Polling

Call the pollApi function to start polling the API.

```
pollApi(apiEndpoint, successResponse, pollingInterval, maxPollingDuration);

```
and voila-it works.

### Recursive Approach over Loop

A recursive function is used in the provided solution rather than a loop. The function makeRequest calls itself using setTimeout to create the delay between API requests. This approach leverages JavaScript's asynchronous capabilities to avoid blocking the main thread while waiting for the next request to be made.

The recursive aspect comes from the makeRequest function calling itself via setTimeout, allowing it to schedule future executions without blocking the main thread. This approach ensures that the next request is only made after the specified interval, maintaining the polling cadence.

This recursive approach is effective for polling in JavaScript, ensuring that the application remains responsive while waiting for the desired API response or the maximum polling duration to be reached.

## Conclusion

In this article, we demonstrated how to implement a polling request method in JavaScript to repeatedly hit an API at 5-second intervals for up to 300 seconds or until a successful response is received. Polling can be an effective way to wait for asynchronous processes on the server and react to their outcomes in real time. With this approach, you can ensure your application remains responsive and capable of handling real-world scenarios that require periodic data checks like payment status, ETA status, etc.