task buffer method

queue.js

function queue(tasks, scope) {
      var slice = Array.prototype.slice,task, on ={}, error;
      function next() {
        if (task = tasks.shift()) {
          task.apply(scope, [next].concat(slice.call(arguments, 0)));
        }else{
          on.done && on.done();
        }
      }
      next.error = function(err){
        error = err || 'unknown error';
        on.error && on.error(err,tasks);
      }
      next.apply(scope, slice.call(arguments, 2));
      return {
        on:function(evtName,fnc){
          on[evtName] = fnc;
          if(error){
             on.error && on.error(error,tasks);
          } else if(tasks.length === 0){
            on.done && on.done();
          }
        }
      }
}