(Node.js) Async Task Chain

Demonstrates how to combine a sequence of asynchronous tasks into a single task chain to be run in a background thread.

Install Chilkat for Node.js and Electron using npm at Chilkat npm packages for Node.js Chilkat npm packages for Electron on Windows, Linux, MacOSX, and ARM

var os = require('os');
if (os.platform() == 'win32') {  
    if (os.arch() == 'ia32') {
        var chilkat = require('@chilkat/ck-node21-win-ia32');
    } else {
        var chilkat = require('@chilkat/ck-node21-win64'); 
    }
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node21-arm');
    } else if (os.arch() == 'x86') {
        var chilkat = require('@chilkat/ck-node21-linux32');
    } else {
        var chilkat = require('@chilkat/ck-node21-linux64');
    }
} else if (os.platform() == 'darwin') {
    if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node21-mac-m1');
    } else {
        var chilkat = require('@chilkat/ck-node21-macosx');
    }
}

function chilkatExample() {

    // All Chilkat classes can be unlocked at once at the beginning of a program
    // by calling UnlockBundle.  It requires a Bundle unlock code.
    var chilkatGlob = new chilkat.Global();
    var success = chilkatGlob.UnlockBundle("Anything for 30-day trial.");
    if (success !== true) {
        console.log(chilkatGlob.LastErrorText);
        return;
    }

    var mailman = new chilkat.MailMan();

    // Set the POP3 server's hostname
    mailman.MailHost = "pop.someMailServer.com";

    // Set the POP3 login/password and any other requirements..
    mailman.PopUsername = "myLogin";
    mailman.PopPassword = "myPassword";
    mailman.PopSsl = true;
    mailman.MailPort = 995;

    // Connect to the POP3 server:
    success = mailman.Pop3BeginSession();
    if (!success) {
        console.log(mailman.LastErrorText);
        return;
    }

    // Get the number of messages in the mailbox.
    var numMessages = mailman.GetMailboxCount();
    if (numMessages == 0) {
        console.log("No email messages in the POP3 mailbox.");
        return;
    }

    var taskChain = new chilkat.TaskChain();

    // Create async task objects to fetch each email message
    // by its sequence number
    var i;
    // task: Task
    var task;

    for (i = 1; i <= numMessages; i++) {

        task = mailman.FetchByMsgnumAsync(i);
        if (mailman.LastMethodSuccess == false) {
            console.log(mailman.LastErrorText);
            return;
        }

        // Append each task to the task chain.
        success = taskChain.Append(task);
        if (!success) {
            console.log(taskChain.LastErrorText);
            return;
        }

    }

    // At this point, no tasks have actually started running.
    // All we've done so far is to create tasks for the work that will be done
    // when the task chain is run.

    // Start the task chain running in a background thread.
    // Each task is run one after the other (on the same background thread) until all tasks have completed.
    // The task chain will stop at the first task that fails.
    taskChain.StopOnFailedTask = true;
    success = taskChain.Run();
    if (!success) {
        console.log(taskChain.LastErrorText);
        return;
    }

    // The application is now free to do anything else
    // while the emails are being downloaded

    // For this example, we'll simply sleep and periodically
    // check to see if the taskchain if finished. 
    while (taskChain.Finished !== true) {

        // Sleep 100 ms.
        taskChain.SleepMs(100);

    }

    // A finished task chain could be one that was canceled, aborted, or truly finished.  

    // If the task chain "completed", then it ran to completion.  A "completed" task will
    // have a StatusInt equal to 7.   If the task finished, but was not completed, then it must've
    // been aborted or canceled:
    if (taskChain.StatusInt !== 7) {
        console.log("Task did not complete.");
        console.log("task chain status: " + taskChain.Status);
        return;
    }

    var email = new chilkat.Email();

    var numTasks = taskChain.NumTasks;
    var taskIdx = 0;

    while ((taskIdx < numTasks)) {

        task = taskChain.GetTask(taskIdx);

        // Load the email object with email downloaded by this task.
        success = email.LoadTaskResult(task);
        if (!success) {
            console.log("Failed to load email object for task.");
        }
        else {
            console.log(email.From + "; " + email.Subject);
        }

        taskIdx = taskIdx+1;
    }


}

chilkatExample();