// call this when we're done.
var done = function(err, result) {
  console.log(result);
};

var EXPENSIVE_OPERATION_ON = function(data, callback) {
  callback(/*error, data, etc*/);
};

var arr = [1,2,3,4],
    i = -1,
    len = arr.length,
    results = [],
    eterator = function(err, result) {
      // store this reference for later.
      var callee = arguments.callee;
      if(err) {
        done(err);
      } else {
        result && results.push(result);
        ++i;
        if(i < len) {
          // release control to the event loop using setTimeout
          // this also resets the stack.
          setTimeout(function() {
            EXPENSIVE_OPERATION_ON(arr[i], callee);
          });
        } else {
          done(results);
        }
      }
    };

eterator();