AsyncPolling

An easy way to run reliable polling without messing with setTimeout.

Here is an article explaining why using setInterval is discouraged, especially when dealing with asynchronous tasks.

Installation

In the browser

With bower:

bower install async-polling

Then include the script:

<script src="bower_components/async-polling/dist/async-polling.min.js"></script>
<script>
// Here you can use the AsyncPolling constructor.
</script> 

In NodeJS

With npm:

npm install async-polling

Then require the module:

var AsyncPolling = require('async-polling');

Usage

Here is the basic usage:

AsyncPolling(function (end) {
    // Do whatever you want.
        
    // Then notify the polling when your job is done:
    end();
    // This will schedule the next call.
}, 3000).run();

You can also send a result to the end callback with the usual signature (error, result). Pass null as first argument when everythin is fine:

var polling = AsyncPolling(function (end) {
    someAsynchroneProcess(function (error, response) {
        if (error) {
            // Notify the error:
            end(error)
            return;
        }
        
        // Do something with the result.
        
        // Then send it to the listeners:
        end(null, result);
    });
}, 3000);
 
polling.on('error', function (error) {
    // The polling encountered an error, handle it here.
});
polling.on('result', function (result) {
    // The polling yielded some result, process it here.
});
 
polling.run(); // Let's start polling.

See also the demo script.

API

Create a polling

var polling = AsyncPolling(pollingFunc, delay);

• pollingFunc(end): [function] The function to run periodically; takes a callback as parameter to notify the end of the process and possibly send a result. It will be bound to the polling object.
• delay: [number(ms)|object] the delay between two calls of pollingFunc. If the type is not number, the .valueOf() method of the object will be called to retrieve the amount of milliseconds.

Run the polling

polling.run();

Stop the polling

polling.stop();

Since the polling function is bound to polling, one can call this.stop() from within the polling function:

AsyncPolling(function (end) {
    // Do some stuff
    
    // Here I want to stop the polling:
    this.stop();
    end();
}, 3000).run();

Listen to events

polling.on(eventName, listener);

• eventName: The name of the event for which we register (run, start, error, result, end, schedule, stop).
• listener: The function to call when the specified event occurs.