XMLHttpRequest not getting initialized?
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Thread: XMLHttpRequest not getting initialized?

  1. #1
    Join Date
    Aug 2007
    Posts
    5

    XMLHttpRequest not getting initialized?

    I am new to AJAX. Could someone please help me with this problem.. its kind of urgent for me to get this working.

    I have a form which when submitted should create an XMLHttpRequest to send the form values to a PHP script. Below is my code for the request.
    On IE I get an error saying 'Type Mismatch' at xmlHttp.onreadystatechange=stateChanged(id);
    As you can see in my function stateChanged(id) I have an else statement to check xmlHttp.readyState. This shows as '0', so the request is not getting initialized. What do I need to change?
    Thanks!

    Code:
    var xmlHttp
    
    function save(id)
    { 
    xmlHttp=GetXmlHttpObject();
    if (xmlHttp==null)
      {
      alert ("Your browser does not support AJAX!");
      return;
      } 
      
    var name = $("desc"+id).value;
    var capacity = $("capacity"+id).value;
    var equipid = $("equip"+id).value;
    
    var params = 'desc='+name+'&capacity='+capacity+'&id='+equipid;
    
    xmlHttp.onreadystatechange=stateChanged(id);
    xmlHttp.open("POST","trialsubmit.php",true);
    xmlHttp.send(params);
    }
    
    function GetXmlHttpObject()
    {
    var xmlHttp=null;
    try
      {
      // Firefox, Opera 8.0+, Safari
      xmlHttp=new XMLHttpRequest();
      }
    catch (e)
      {
      // Internet Explorer
      try
        {
        xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
        }
      catch (e)
        {
        xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
      }
    return xmlHttp;
    }
    
    function stateChanged(id) 
    { 
    if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
    { 
    $("name"+id).innerHTML=xmlHttp.responseText;
    }
    else
     { 
      $("name"+id).innerHTML=xmlHttp.readyState;
     }
    }

  2. #2
    Join Date
    Nov 2005
    Posts
    49

    Re: XMLHttpRequest not getting initialized?

    i think onreadystatechange takes a function with no argument. If you have to send argument then use this line of code:

    Code:
    httpReq.onreadystatechange = function (){showAjaxData(httpReq, id)};
    Muhammad Waqas Badar

  3. #3
    Join Date
    Jul 2007
    Location
    Sweden
    Posts
    331

    Re: XMLHttpRequest not getting initialized?

    To further elaborate on what Waqas_Badar wrote, doing the following assignment:
    Code:
    xmlHttp.onreadystatechange = stateChanged(id);
    will run stateChanged(id) immediately and assign its return value to xmlHttp.onreadystatechange. To assign a variable to a reference to a function instead of the return value of a function, you can't use parentheses:
    Code:
    xmlHttp.onreadystatechange = stateChanged;
    If you have to pass values to the function, you should do what Waqas_Badar suggested:
    Code:
    httpReq.onreadystatechange = function () { stateChanged(id); };

  4. #4
    Join Date
    Aug 2007
    Posts
    5

    Re: XMLHttpRequest not getting initialized?

    That was it.. thanks!

  5. #5
    Join Date
    Aug 2005
    Location
    Milwaukee, WI
    Posts
    55

    Re: XMLHttpRequest not getting initialized?

    I realize you've found your solution, but there is another possibility that is helpful sometimes:

    Code:
    function save(id)
    {
    ...
    
    xmlHttp.onreadystatechange = stateChanged;
    xmlHttp.id = id; ... } function stateChanged() { //this points to the xmlHttp object var id = this.id .... }
    I usually do it this way because I think it is a little "cleaner", but it is a matter of aesthetics.

  6. #6
    Join Date
    Jul 2007
    Location
    Sweden
    Posts
    331

    Re: XMLHttpRequest not getting initialized?

    I generally avoid setting properties of objects I haven't constructed myself (unless they're actually proper extensions to those objects.) I'd rather go with a manager class if there's more complex variable sending going on:

    Code:
    var Request = function (id) {
        this.id = id;
    };
    
    Request.prototype = {
        id: -1,
    
        stateChange: function () {
            // thanks to call(), "this" refers to the current instance.
            // ...
        },
    
        send: function () {
            var http = GetXmlHttpObject();
    
            var t = this;
            http.onreadystatechange = function () { t.stateChange.call(t); };
    
            // Use instance variables here...
            http.open("GET", "index.html", true);
            http.send("");
        }
    };
    
    var req = new Request(10);
    req.send();

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