Tips for creating a sophisticated JavaScript polling system

In order to meet my requirement, I am looking for a JavaScript function that can continuously poll the database via AJAX to check for a specific status. When the status is "active," I want an alert to notify me that the case is now active. The JavaScript should check the database every 2 seconds until it returns the "active" status. Can you suggest an elegant and efficient solution for this task? Below is a sample JavaScript code snippet outlining what I aim to accomplish:

function ReportAsActivePoll()
{
   for(var i=0; i<10; i++)
   { 
      setTimeout(StatusIsActive,(i*2000));
      if(statusIsActive)
      {
         ReportAsActive();
         break;
      }
   }
}

var statusIsActive = false;
function StatusIsActive(case)
{
   statusIsActive = GetStatusFromDB(case) == "active";
}

function ReportAsActive()
{
   alert("case is now active")
}

Some additional points to consider:

  • I acknowledge that the provided code snippet is not entirely accurate - it serves as a visual aid only.
  • The current implementation will invoke StatusIsActive 10 times in total. My intention is to terminate these calls once the status becomes active. However, due to the nature of polling, I understand that all calls need to be queued up beforehand, presenting a challenge in terms of stopping the process prematurely.

Answer №1

One way to achieve simplicity is by using setInterval() and clearInterval(). Here's an example:

<script type="text/javascript">

function checkStatus(theCase) {
    var intervalId = window.setInterval(function() {
        if (getStatusFromDb(theCase) == 'active') {
            clearInterval(intervalId)
            reportAsActive()
        }
    }, 2000)
}
function reportAsActive()
{
   alert("The case is now active")
}

var tmpCounter = 0
function getStatusFromDb(theCase)
{
    if (tmpCounter++ == 4) return "active"
}
checkStatus('case 123')

</script>

It's also recommended to follow the normal JS convention of starting function names with a lowercase letter. Deviating from this standard can lead to hard-to-find case-sensitive errors.

Answer №2

To ensure effective communication between your application and the server, it is recommended to utilize setInterval instead of setTimeout. This allows you to continuously poll the server for updates until a valid response is received, at which point you can use clearInterval to stop the polling process.

Here's an example code snippet to achieve this:

var intervalID = window.setInterval(function(){
  var resFromYourDB = ...; // fetch data from server using ajax
  if (resFromYourDB['active']){
     window.clearInterval(intervalID);
     // perform necessary action upon receiving valid response
  }
}, 2000)

By implementing this approach, your application will continuously check for the 'active' status in the server response without relying on a fixed time duration like with setTimeout. Once the desired response is obtained, the polling mechanism will be gracefully stopped.

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