Callback Functions

<button id="brew">Brew</button>

//init when window loaded
function init() {

    document.getElementById('brew').onclick = function() {
        brew(param, function() {
            alert('Finished brewing ' + param + ' coffee');
        });                    

    };

    var param = 'dark roast';

    function brew(param, callback) {
        alert('Started brewing ' + param + ' coffee');
        callback();
    };

}
window.onload = init;