This function can be used to sync many asynchronous functions. You only have to maintain the list and order once, and they will execute one after the other, as well as a callback after all the functions are done.

sync.js

function firstFunction(next){
  console.log('first function');
  setTimeout(next, 1000);
}

function secondFunction(next){
  console.log('second function');
  setTimeout(next, 1000);
}

function sync(funcs, done){
  var counter = funcs.length;
  var idx = 0;
        
  var next = function() {
    if (--counter === 0) done();
    else funcs[idx++](next);
  };
        
  funcs[idx++](next);
}
  
function over(){ console.log('async functions are over') };
    
sync([firstFunction, secondFunction], over);