console.clear();
console.log("a");
setTimeout(function(){console.log("b");},1000);
console.log("c");
setTimeout(function(){console.log("d");},0);

function downloadFile(filePath, callback)
{
  blah.downloadFile(filePath);
  callback();
}

//Let's say this code is running in tick 1
fs.readFile("/home/barney/colors.txt", function (error, data) {
  //The code inside this callback function will absolutely NOT run in tick 1
  //It will run in some tick >= 2
});
//This code will absolutely also run in tick 1
//HOWEVER, typically there's not much else to do here,
//so at some point soon after queueing up some async IO, this tick
//will have nothing useful to do so it will just end because the IO result
//is necessary before anything useful can be done

console.clear();                                   //exec sync
console.log("a");                                  //exec sync
setTimeout(                //schedule inAWhile to be executed at now +1 s
    function inAWhile(){
        console.log("b");
    },1000);
console.log("c");                                  //exec sync
setTimeout(
    function justNow(){          //schedule justNow to be executed just now
        console.log("d");
},0);