I've written a short snippet of code to replace JQuery's $.post ( to get ride of JQuery, mainly ). The function does seem to work. But, since I might be using this function in a couple of other pages, I'm just hoping to get a general review of the code.

I'm not confident the parameter formatting is done properly ( I couldn't find a lot of information on the web concerning how to pass parameters to .send( ). So if anyone sees that I have done it correctly or not, that would help.

Here's the code:

function FileRequest(data, successFunction) {
    request = new XMLHttpRequest();
  else request = new ActiveXObject("Microsoft.XMLHTTP");
  request.onreadystatechange = function () {
    if((request.readyState == 4) && (request.status == 200)) {
      if(typeof (successFunction) == "function") successFunction(request.responseText);
  request.open("POST", "fileHandler.php", true);
  if(typeof (data) != "undefined") {
    var parameterNames = ["command=",
      parameters = "";
    for(var i = 0; data[i] && (i < 3); i++) {
      parameters += parameterNames[i] + encodeURI(data[i]);
      if(data[i + 1]) parameters += "&";
    request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    request.setRequestHeader("Content-length", parameters.length);
  } else request.send();

Here's an example of it's use:

FileRequest(["load", "Projects/test.c"], function (data) {

1 Answer 1


First of all, I'd suggest you use a library for several reasons:

  • It's abstracted a lot of cross-browser differences

  • Spread the task of the code to the community. That way you focus more on the task at hand, rather than fixing some bugs.

  • More event and processing support, like on errors, on complete, on success, on beforesend and others.

Anyways, moving to your code

function FileRequest(data, successFunction) {

  //The compiler pulls up variable and function declarations.
  //To avoid visibility confusion, we'll write them that way as well
  var parameters = '';
  var key;

  if(window.XMLHttpRequest)request = new XMLHttpRequest();
  else request = new ActiveXObject("Microsoft.XMLHTTP");

  request.onreadystatechange = function () {
    //the early return pattern is best to avoid deep indention
    //so if the request isn't complete and successful, return
    //also, always use strict comparison when possible
    if(!(request.readyState === 4 && request.status === 200)) return;

    if(typeof successFunction === "function") successFunction(request.responseText);

  //the third parameter defaults to true so we can omit
  request.open("POST", "fileHandler.php");

  //for scalability, you should not hard-code the parameter names
  //allow the user of the API to define the data name.
  //thus we use objects, and the for-in loop

  //since we use objects, we'll have to check if it is
  //the simplest check is to check if it's not null, it's an object but not an array
  if(data && typeof data === 'object' && !(data instanceof Array)){

    for(key in data){
      //similar to early-return pattern, the early continue
      //which skips early if we the condition is met.
      //if the key isn't from the data but from prototype, we skip
      if(!data.hasOwnProperty(key)) continue;

      //append to parameters
      parameters += key + '=' + encodeURI(data[key]) + '&';

    request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    request.setRequestHeader("Content-length", parameters.length);

  //so we send either a blank or something

    command : 'load',
    arg1 : 'Projects/test.c'
  function (data){
    //when debugging, use console.log if the browser supports it
  • \$\begingroup\$ Thanks Joseph, that helps a lot. I agree with your points about using libraries. I usually just re-implement these functions just for practice, mainly. \$\endgroup\$
    – tay10r
    May 11, 2013 at 5:21
  • 1
    \$\begingroup\$ I also noticed that you removed encodeURI( ) from the parameter data. I think that should still be there, if you get a chance \$\endgroup\$
    – tay10r
    May 11, 2013 at 5:25
  • \$\begingroup\$ @TaylorFlores yup, seem to have missed that. \$\endgroup\$
    – Joseph
    May 11, 2013 at 5:35

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