var markdown_editor = function (labfile, markdown) {
  var markdown_arr = Object.keys(markdown);

  var mapping = markdown_arr.map(function(task_name) {
    var task_md = markdown[task_name];
    var md_finder = new RegExp("\/\\*( |\n)*?@(" + task_name.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&") + ")( |\n)((.|\n)*?)\\*\/","gm");
    return [labfile.match(md_finder)[0], "/*@" + task_name + "\n" + task_md + "*/"];
  });
  var result = labfile;
  mapping.forEach(function(arr) { result = result.replace(arr[0],arr[1]);});
  return result;
};

var labfile = "hi im bob\n/*@potato this is old potato right here.*/ momo /*@orange\nold orange here */";
var markdown = {potato: "new potato", orange: "new orange is:\nthis"};
var res = markdown_editor(labfile,markdown);
console.log(res);