Question

I have a javascript that takes about 2 seconds to execute (complex optimization algorithm).
I want to set certain span to “working…” at the beginning of the function.
I observe that the span doesn’t change until the end of the function.

How can I force DOM changes propagation? or should I approach this differently all together?

I call the function from onclick on the button.

The function is something like:

function optimize() {
    $('#status').text('working...');
    // calculate for 2 seconds
    $('#status').text('done!');
}

Answer 1

Try wrapping the long running code in a setTimeout call:

function optimize() {
    $('#status').text('working...');
    window.setTimeout(function() {
        // calculate for 2 seconds
        $('#status').text('done!');
    }, 0);
}

This forces a new call stack for the long running code, allowing the repaint (changing of the text) to complete before the new call stack begins execution.