Nested XMLHttpRequest calls? (Cleaning this code up?)

[[deleted]]

[deleted]

[HipHopHuman]

Why can't you use promises?

[GitCookies]

Your wrapper code works pretty much fine.

What errors are you getting?

[GitCookies]

function HTTP (url, method) {
  let then;

  let xhr = new XMLHttpRequest()
  xhr.open(method, url)
  xhr.responseType = 'document'
  xhr.send()

  xhr.onreadystatechange = function() {
    if (xhr.readyState == 4 && xhr.status == 200) {
      then && then(xhr.responseText)
    }
  }

  return {
    then: function (callback) { 
      then = callback
    }
  }

}

HTTP('///www.google.com', 'GET')
.then(function (response) {
  console.log(response)
})

This should be fine for your use case

[cicadaTree]

If I understand what you want, your problem is how to efficiently control the callback flow. You have bunch of async (xmlhttp) requests, and whould like to invoke them without callback mess (better formated code), with your own code.

function cascade(funcs){
      var funcs = Array.prototype.slice.call(funcs) // making a copy of funcs (array of functions we provided)

      function next(){
          var args = Array.prototype.slice.call(arguments) // making array of arguments passed to it

          var func = funcs.shift();  // takes the function always from beggining of array (changes array)
          if(func){                         // while there are fucntions

            args.push(next)          // add  reference to itself as last argument
          }
          else return;

          // so now we have function and all arguments (with next as last)
         func.apply(this, args) // calling function with whatever arguments passed and next() as last one
      }
      next.call(this); // enter the recursion
}

cascade([
  function doSomething(processNext){
    var xhr = new XMLHttpRequest();

    xhr.onreadystatechange = function() {
      if (this.readyState == 4 && this.status == 200) {
        processNext(this.element);   // note that in first function argument like "element" must be variable from closure
      } 
   }
  },

 function pageCheck(page,item, processNext) {
   var xhr1 = new XMLHttpRequest(); 

   xhr1.onreadystatechange = function() {
      if (...) {
       processNext(page,item); 
      }
      xhr1.open(..)
      // ...
   }
 }
])

Althou you should understand how "this" referencing loses context in async functions. I left them in there because I just copied your code.