var btn = document.getElementById("btn");

btn.addEventListener("click", handler, false);

function handler(e) {
  console.log("handler triggered");
  doSomething();
  console.log("handler done");
}

function doSomething() {
  doThis();
  doThat();
  doTheOther();
}

function doThis() {
  console.log("doThis - start & end");
}
function doThat() {
  console.log("doThat - start");
  // do something that takes a while
  var stop = Date.now() + 1000;
  while (Date.now() < stop) {
    // wait
  }
  console.log("doThat - end");
}
function doTheOther() {
  console.log("doThat - start & end");
}