Not All Tasks Created Equal!

All programs are seen as composed of control structures, ordered statements or subroutines, executed in sequence.

function task(id) {
  console.log("Task " + id);
}

task(1);
task(2);
task(3);
task(4);

What will happen when one task (subroutine) takes a long time to complete?

function task(id) {
  console.log("Task " + id);
}

function longtask(id) {
  console.log("Task " + id + " started!");
  for(let i = 0; i < 3e9; i++) {
    // do something!
  }
  console.log("Task " + id + " finished!");
}

task(1);
longtask(2);
task(3);
task(4);

The long (resource intensive) task appears to block the ones that follow!

What are the implications of this for event-driven applications such as web apps?

Well, as long as the "long task" is running, all other things are blocked! The web app will appear unresponsive or frozen!