requestIdleCallback usage pattern that simplifies things a tiny bit

requestIdleStack.js

//always include a polyfill that falls back to setTimeout(cb,1) https://gist.github.com/paullewis/55efe5d6f05434a96c36 
//or possibly something better https://github.com/PixelsCommander/requestIdleCallback-polyfill

//calling this function creates and returns a new stack of idle functions, 
//and exposes an addTasks method that will add more to the stack as needed and return a cancelIdleCallback cancelable id
function createIdleStack(){
  var bgtasks = [];//array of all tasks

  function backgroundTask(deadline){
    //does each task in order, checking to see if there's time left
    while ((deadline.timeRemaining() > 0  || deadline.didTimeout) && bgtasks.length > 0) {
      bgtasks.shift()();
    }
    if (bgtasks.length > 0) {
      requestIdleCallback(backgroundTask,{timeout:bgtasks.timeout});
    }
  }

  //method of adding tasks to the stack, with optional last "timeout" parameter
  bgtasks.addTasks = function(/*...tasks, optional ops*/){
    var args = Array.prototype.slice.call(arguments),//or Array.from
        cachedLength = bgtasks.length;

    bgtasks.timeout = (args.length && args[args.length-1].timeout)? args.pop().timeout : {};
    
    if(args.length){
      bgtasks.push.apply(bgtasks,args);
      if(!cachedLength || !bgtasks.id){//if the stack is clear or there's no callbackid, create a new stack
        return bgtasks.id = requestIdleCallback(backgroundTask,{timeout:bgtasks.timeout});
      }else{
        return bgtasks.id;//otherwise just return the existing id, there's already a callback in the wild
      }
    }else{
      throw Error('no tasks');
    }
  };
  //returns an id that can be used to cancel this entire stack, if needed

  return bgtasks;
}

//USAGE
//var idleStack = createIdleStack();
//var cancel = idleStack.addTasks(function(){console.log('test')},function(){console.log('test2')});
//var cancel = idleStack.addTasks(function(){console.log('test3')},function(){console.log('test4')});
////cancelIdleCallback(cancel);//if run immediately or soon enough after adding tasks, will cancel everything remaining

//otherwise, functions passed as arguments passed to addTasks will get queued up to run when there's time. 
//If you plan to cancel a stack, make sure to update the id with each new call to addTasks
//you can't really _know_ whether or not the first call will have completed, so it may have made a new call