JavaScript/AJAX Functionality Only Operates Correctly During Debugging

I am currently facing an issue with dynamically populating a website. The code works perfectly when I step through it, but it fails to work as intended on page load. Here is the relevant code snippet:

<body onload="populate_all(string)";>

function populate_all(string)
{
  var split = string.split(" ");
  for(i = 0; i < split.length; i++)
  {
    populate(split[i], 'main'); 
  }
} 

function populate(string, location)
{
  if (string.length==0)
  { 
   document.getElementById(location).innerHTML="";
   return;
  }

  if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
   xmlhttp=new XMLHttpRequest();
  }
  else
  {// code for IE6, IE5
   xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }

  xmlhttp.onreadystatechange=function()
 {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
  {
        var divTag = document.createElement("div");

        divTag.className ="info";

        divTag.innerHTML = xmlhttp.responseText;

        document.getElementById(location).appendChild(divTag);
  }
 }
 xmlhttp.open("GET","populate.php?string="+string,true);
 xmlhttp.send();
 }

After researching the issue, I believe the problem does not lie within the php code. Essentially, my JavaScript function using AJAX runs multiple times in a loop and only functions properly when debugging. Any assistance would be greatly appreciated. Thank you!

Answer №1

  1. Make sure to declare xmlhttp at a local level.
  2. It is advisable to use a unique variable name instead of location. The global variable location contains properties and methods for manipulating the current location.

    function updateContent(string, s_location) {
        var xmlhttp;
    

Be mindful that repeatedly reassigning the xmlhttp variable within the updateContent function can lead to confusion. This practice causes the xmlhttp object to reference the most recent request made.

Answer №2

One solution that worked for me is detailed in this forum post: Using JavaScript variable outside of success function

While working on calls to $.getJSON and similar functions, I encountered timing and scoping issues which were resolved when I attached a debugger. This allowed me to update a table cell value based on an xhr response triggered by background events with precise control over when the updates occurred in nested success functions. The magic of debugging made everything fall into place.

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