display message javascript while a calculation is

Question

I have been looking around and I cannot seem to figure out how to do this, although it seems like it would be very simple.(mobile development)

What I am trying to do is display a message (kind of like an alert, but not an alert, more like a dialog) while a calculation is being made. Simply like a Loading please wait. I want the message to appear and stay there while the calculation is being done and then be removed. I just cannot seem to find a proper way of doing this.

The submit button is pressed and first checks to make sure all the forms are filled out then it should show the message, it does the calculation, then hides the message.

Here is the Calculation function.

   function scpdResults(form) {
        //call all of the "choice" functions here
        //otherwise, when the page is refreshed, the pulldown might not match the variable
        //this shouldn't be a problem, but this is the defensive way to code it
        choiceVoltage(form);
        choiceMotorRatingVal(form);
        getMotorRatingType();
        getProduct();
        getConnection();
        getDisconnect();
        getDisclaimer();
        getMotorType();

        //restore these fields to their default values every time submit is clicked
        //this puts the results table into a known state
        //it is also used in error checking in the populateResults function
        document.getElementById('results').innerHTML = "Results:";
        document.getElementById('fuse_cb_sel').innerHTML = "Fuse/CB 1:";
        document.getElementById('fuse_cb_sel_2').innerHTML = "Fuse/CB 2:";
        document.getElementById('fuse_cb_result').innerHTML = "(result1)";
        document.getElementById('fuse_cb_res_2').innerHTML = "(result2)";
        document.getElementById('sccr_2').innerHTML = "<b>Fault Rating:</b>";
        document.getElementById('sccr_result').innerHTML = "(result)";
        document.getElementById('sccr_result_2').innerHTML = "(result)";
        document.getElementById('contactor_result').innerHTML = "(result)";
        document.getElementById('controller_result').innerHTML = "(result)";

        //Make sure something has been selected for each variable
        if (product === "Choose an Option." || product === "") {
            alert("You must select a value for every field.  Select a Value for Product");
        **************BLAH************
        } else {

            //valid entries, so jump to results table
            document.location.href = '#results_a';


    ******This is where the message should start being displayed***********

            document.getElementById('motor_result').innerHTML = motorRatingVal + " " + motorRatingType;
            document.getElementById('voltage_res_2').innerHTML = voltage + " V";
            document.getElementById('product_res_2').innerHTML = product;
            document.getElementById('connection_res_2').innerHTML = connection;
            document.getElementById('disconnect_res_2').innerHTML = disconnect;

            if (BLAH) {

            }
            else {

            }

            populateResults();
            document.getElementById('CalculatedResults').style.display = "block";

        } //end massive else statement that ensures all fields have values


*****Close out of the Loading message********
    } //scpd results

Thank you all for your time, it is greatly appreciated

Answer 1

You need to give the UI main thread a chance to render your message before starting your calculation.

This is often done like this:

showMessage();
setTimeout(function() {
    doCalculation();
    cleanUp()
}, 0);

Using the timer allows the code to fall through into the event loop, update the UI, and then start up the calculation.

Answer 2

It is a good idea to separate your display code from the calculation code. It should roughly look like this

displayDialog();
makeCalculation();
closeDialog();

If you are having trouble with any of those steps, please add it to your question.

Answer 3

You're already using a section to pop up a "results" page -- why not pop up a "calculating" page?

Really, there are 4,000,000 different ways of tackling this problem, but why not try writing a "displayCalculatingMessage" function and a "removeCalculatingMessage" function, if you don't want to get all object-oriented on such a simple thing.

function displayCalculatingMessage () {
    var submit_button = getSubmitButton();
    submit_button.disabled = true;

    // optionally get all inputs and disable those, as well

    // now, you can either do something like pop up another hidden div,
    // that has the loading message in it...
    // or you could do something like:
    var loading_span = document.createElement("span");
    loading_span.id = "loading-message";
    loading_span.innerText = "working...";

    submit_button.parentElement.replaceChild(loading_span, submit_button);
}

function removeCalculatingMessage () {
    var submit_button = getSubmitButton(),
        loading_span = document.getElementById("loading-message");

    submit_button.disabled = false;
    loading_span.parentElement.replaceChild(submit_button, loading_span);

    // and then reenable any other disabled elements, et cetera.
    // then bring up your results div...
    // ...or bring up your results div and do this after
}

There are a billion ways of accomplishing this, it all comes down to how you want it to appear to the user -- WHAT you want to have happen.

Answer 4

Computers are fast. Really fast. Most modern computers can do several billion instructions per second. Therefore, I'm fairly certain you can rely on a a setTimeout function to fire around 1000ms to be sufficient to show a loading message.

if (product === "Choose an Option." || product === "") {
  /* ... */
} else {
  /* ... */
  var loader = document.getElementById('loader');
  loader.style.display = 'block';
  window.setTimeout(function() {
    loader.style.display = 'none';
    document.getElementById('CalculatedResults').style.display = "block";
  }, 1000);
}

<div id="loader" style="display: none;">Please wait while we calculate.</div>