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JavaScript SOAP Client

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24 Jan 20064 min read 1.1M   17.4K   140   174
Using AJAX to call a Web Service.

Introduction

A lot of talking about AJAX is taking place here and there; AJAX is the acronym of "Asynchronous JavaScript and XML", a technology based on XMLHttpRequest, which is now supported by all main browsers. The basic idea is quite simple - and not actually a breakthrough - but it allows updating a page following a server request, without reloading the entire set of data. Some examples can be found on GMail or Google Suggest. For additional information about AJAX, you can see Wikipedia.

In this article, we propose a solution based on AJAX that has a great advantage with respect to those commonly found in Internet: calls are made to the Web Services.

This permits:

  1. On the server side, we only have to expose a Web Service with the required methods (instead of generating dynamic pages incorporating data that are based on a custom syntax or on a generic XML).
  2. On the client side, we use the WSDL (Web Service Description Language) to automatically generate a JavaScript proxy class so as to allow using the Web Service return types - that is similar to what Visual Studio does when a Web Reference is added to the solution.

The following diagram shows the SOAP Client workflow for asynchronous calls:

Image 1

The Client invokes the "SOAPClient.invoke" method using a JavaScript function and specifies the following:

  • Web Service URL (please note that many browsers do not allow cross-domain calls for security reasons).
  • Web method name.
  • Web method parameter values.
  • Call mode (async = true, sync = false).
  • Callback method invoked upon response reception (optional for sync calls).

The "SOAPClient.invoke" method executes the following operations (numbers refer to the previous diagram):

  1. It gets the WSDL and caches the description for future requests.
  2. It prepares and sends a SOAP (v. 1.1) request to the server (invoking method and parameter values).
  3. It processes the server reply using the WSDL so as to build the corresponding JavaScript objects to be returned.
  4. If the call mode is async, the callback method is invoked, otherwise it returns the corresponding object.

Using the code

After having exposed our idea about consuming a Web Service via JavaScript, we only have to analyze the code.

Let's start with the class for the definition of the parameters to be passed to the Web method: "SOAPClientParameters":

JavaScript
function SOAPClientParameters()
{
    var _pl = new Array();
    this.add = function(name, value) 
    {
        _pl[name] = value; 
        return this; 
    }
    this.toXml = function()
    {
        var xml = "";
        for(var p in _pl)
        {
            if(typeof(_pl[p]) != "function")
                xml += "<" + p + ">" + 
                       _pl[p].toString().replace(/&/g, 
                         "&").replace(/</g, 
                         "<").replace(/>/g, 
                         ">

The code simply consists of an internal dictionary (associative array) with the parameter name (key) and the related value; the "add" method allows appending new parameters, while the "toXml" method provides XML serialization for SOAP requests (see "SOAPClient._sendSoapRequest").

Let's define the "SOAPClient" class, which can only contain static methods in order to allow async calls, and the only "public" method within this class: "SOAPClient.invoke".

Note: since JavaScript does not foresee access modifiers - such as "public", "private", "protected", etc. - we'll use the "_" prefix to indicate private methods.

JavaScript
function SOAPClient() {}
SOAPClient.invoke = function(url, method, 
                      parameters, async, callback)
{
    if(async)
        SOAPClient._loadWsdl(url, method, 
                    parameters, async, callback);
    else
        return SOAPClient._loadWsdl(url, method, 
                   parameters, async, callback);
}

The "SOAPClient.invoke" method interface is described above; our implementation checks whether the call is async (call result will be passed to the callback method) or sync (call result will be directly returned). The call to the Web Service begins by invoking the "SOAPClient._loadWsdl" method:

JavaScript
SOAPClient._loadWsdl = function(url, method, parameters, async, callback)
{
    // load from cache?
    var wsdl = SOAPClient_cacheWsdl[url];
    if(wsdl + "" != "" && wsdl + "" != "undefined")
        return SOAPClient._sendSoapRequest(url, method, 
                    parameters, async, callback, wsdl);
    // get wsdl
    var xmlHttp = SOAPClient._getXmlHttp();
    xmlHttp.open("GET", url + "?wsdl", async);
    if(async) 
    {
        xmlHttp.onreadystatechange = function() 
        {
            if(xmlHttp.readyState == 4)
                SOAPClient._onLoadWsdl(url, method, 
                     parameters, async, callback, xmlHttp);
        }
    }
    xmlHttp.send(null);
    if (!async)
        return SOAPClient._onLoadWsdl(url, method, parameters, 
                                    async, callback, xmlHttp);
}

The method searches the cache for the same WSDL in order to avoid repetitive calls:

JavaScript
SOAPClient_cacheWsdl = new Array();

If the WSDL is not found in the cache (it's the first call in the current context), it is requested from the server using an XMLHttpRequest, according to the required mode (sync or not). Once an answer is obtained from the server, the "SOAPClient._onLoadWsdl" method is invoked:

JavaScript
SOAPClient._onLoadWsdl = function(url, method, 
             parameters, async, callback, req)
{
    var wsdl = req.responseXML;
    SOAPClient_cacheWsdl[url] = wsdl;
    return SOAPClient._sendSoapRequest(url, method, 
                       parameters, async, callback, wsdl);
}

A WSDL copy is stored into the cache and then the "SOAPClient._sendSoapRequest" method is executed:

JavaScript
SOAPClient._sendSoapRequest = function(url, method, 
                 parameters, async, callback, wsdl)
{
    var ns = (wsdl.documentElement.attributes["targetNamespace"] + 
              "" == "undefined") ? 
              wsdl.documentElement.attributes.getNamedItem(
              "targetNamespace").nodeValue : 
              wsdl.documentElement.attributes["targetNamespace"].value;
    var sr = 
        "<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
        "<soap:Envelope " +
        "xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" " +
        "xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" " +
        "xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">" +
        "<soap:Body>" +
        "<" + method + " xmlns=\"" + ns + "\">" +
        parameters.toXml() +
        "</" + method + "></soap:Body></soap:Envelope>";
    var xmlHttp = SOAPClient._getXmlHttp();
    xmlHttp.open("POST", url, async);
    var soapaction = 
      ((ns.lastIndexOf("/") != ns.length - 1) ? ns + "/" : ns) + method;
    xmlHttp.setRequestHeader("SOAPAction", soapaction);
    xmlHttp.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
    if(async) 
    {
        xmlHttp.onreadystatechange = function() 
        {
            if(xmlHttp.readyState == 4)
                SOAPClient._onSendSoapRequest(method, 
                     async, callback, wsdl, xmlHttp);
        }
    }
    xmlHttp.send(sr);
    if (!async)
        return SOAPClient._onSendSoapRequest(method, 
                    async, callback, wsdl, xmlHttp);
}

The service namespace is taken out of the WSDL (using different XPath queries for Internet Explorer and Mozilla / FireFox), then a SOAP v. 1.1 request is created and submitted. The "SOAPClient._onSendSoapRequest" method will be invoked upon receiving the server response:

JavaScript
SOAPClient._onSendSoapRequest = function(method, 
                     async, callback, wsdl, req)
{
    var o = null;
    var nd = SOAPClient._getElementsByTagName(
             req.responseXML, method + "Result");
    if(nd.length == 0)
    {
        if(req.responseXML.getElementsByTagName(
                     "faultcode").length > 0)
            throw new Error(500, 
              req.responseXML.getElementsByTagName(
              "faultstring")[0].childNodes[0].nodeValue);
    }
    else
        o = SOAPClient._soapresult2object(nd[0], wsdl);
    if(callback)
        callback(o, req.responseXML);
    if(!async)
        return o;        
}

The server response is processed looking for faults: if found, an error is raised. Instead, if a correct result is obtained, a recursive function will generate the return type by using the service description:

JavaScript
SOAPClient._soapresult2object = function(node, wsdl)
{
    return SOAPClient._node2object(node, wsdl);
}

SOAPClient._node2object = function(node, wsdl)
{
    // null node
    if(node == null)
        return null;
    // text node
    if(node.nodeType == 3 || node.nodeType == 4)
        return SOAPClient._extractValue(node, wsdl);
    // leaf node
    if (node.childNodes.length == 1 && 
       (node.childNodes[0].nodeType == 3 || 
        node.childNodes[0].nodeType == 4))
          return SOAPClient._node2object(node.childNodes[0], wsdl);
    var isarray = SOAPClient._getTypeFromWsdl(node.nodeName, 
                  wsdl).toLowerCase().indexOf("arrayof") != -1;
    // object node
    if(!isarray)
    {
        var obj = null;
        if(node.hasChildNodes())
            obj = new Object();
        for(var i = 0; i < node.childNodes.length; i++)
        {
            var p = SOAPClient._node2object(node.childNodes[i], wsdl);
            obj[node.childNodes[i].nodeName] = p;
        }
        return obj;
    }
    // list node
    else
    {
        // create node ref
        var l = new Array();
        for(var i = 0; i < node.childNodes.length; i++)
            l[l.length] = 
              SOAPClient._node2object(node.childNodes[i], wsdl);
        return l;
    }
    return null;
}

SOAPClient._extractValue = function(node, wsdl)
{
    var value = node.nodeValue;
    switch(SOAPClient._getTypeFromWsdl(
           node.parentNode.nodeName, wsdl).toLowerCase())
    {
        default:
        case "s:string":            
            return (value != null) ? value + "" : "";
        case "s:boolean":
            return value+"" == "true";
        case "s:int":
        case "s:long":
            return (value != null) ? parseInt(value + "", 10) : 0;
        case "s:double":
            return (value != null) ? parseFloat(value + "") : 0;
        case "s:datetime":
            if(value == null)
                return null;
            else
            {
                value = value + "";
                value = value.substring(0, value.lastIndexOf("."));
                value = value.replace(/T/gi," ");
                value = value.replace(/-/gi,"/");
                var d = new Date();
                d.setTime(Date.parse(value));                                        
                return d;                
            }
    }
}
SOAPClient._getTypeFromWsdl = function(elementname, wsdl)
{
    var ell = wsdl.getElementsByTagName("s:element");    // IE
    if(ell.length == 0)
        ell = wsdl.getElementsByTagName("element");    // MOZ
    for(var i = 0; i < ell.length; i++)
    {
        if(ell[i].attributes["name"] + "" == "undefined")    // IE
        {
            if(ell[i].attributes.getNamedItem("name") != null && 
               ell[i].attributes.getNamedItem("name").nodeValue == 
               elementname && ell[i].attributes.getNamedItem("type") != null) 
                return ell[i].attributes.getNamedItem("type").nodeValue;
        }    
        else // MOZ
        {
            if(ell[i].attributes["name"] != null && 
               ell[i].attributes["name"].value == 
               elementname && ell[i].attributes["type"] != null)
                return ell[i].attributes["type"].value;
        }
    }
    return "";
}

The "SOAPClient._getElementsByTagName" method optimizes XPath queries according to the available XML parser:

JavaScript
SOAPClient._getElementsByTagName = function(document, tagName)
{
    try
    {
        return document.selectNodes(".//*[local-name()=\""+ 
                                           tagName +"\"]");
    }
    catch (ex) {}
    return document.getElementsByTagName(tagName);
}

A factory function returns the XMLHttpRequest according to the browser type:

JavaScript
SOAPClient._getXmlHttp = function() 
{
    try
    {
        if(window.XMLHttpRequest) 
        {
            var req = new XMLHttpRequest();
            if(req.readyState == null) 
            {
                req.readyState = 1;
                req.addEventListener("load", 
                    function() 
                    {
                        req.readyState = 4;
                        if(typeof req.onreadystatechange == "function")
                            req.onreadystatechange();
                    },
                    false);
            }
            return req;
        }
        if(window.ActiveXObject) 
            return new ActiveXObject(SOAPClient._getXmlHttpProgID());
    }
    catch (ex) {}
    throw new Error("Your browser does not support XmlHttp objects");
}

SOAPClient._getXmlHttpProgID = function()
{
    if(SOAPClient._getXmlHttpProgID.progid)
        return SOAPClient._getXmlHttpProgID.progid;
    var progids = ["Msxml2.XMLHTTP.5.0", 
                   "Msxml2.XMLHTTP.4.0", 
                   "MSXML2.XMLHTTP.3.0", 
                   "MSXML2.XMLHTTP", 
                   "Microsoft.XMLHTTP"];
    var o;
    for(var i = 0; i < progids.length; i++)
    {
        try
        {
            o = new ActiveXObject(progids[i]);
            return SOAPClient._getXmlHttpProgID.progid = progids[i];
        }
        catch (ex) {};
    }
    throw new Error("Could not find an installed XML parser");
}

Points of Interest

By using a single little (less than 10 KB) JavaScript library and, on the server side, simply exposing a Web Service with remote methods, you can use AJAX to create dynamic Web applications with no need for reloading the entire page.

See the on-line demo for an example of usage.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


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Comments and Discussions

 
GeneralRe: wsdl in client Pin
h3ll5ing7-Sep-10 5:50
h3ll5ing7-Sep-10 5:50 
Generalproblem with the request Pin
andré brunelli28-Jul-09 5:40
andré brunelli28-Jul-09 5:40 
GeneralProblem to get the response from the web service Pin
Matrix818181813-Jun-09 8:22
Matrix818181813-Jun-09 8:22 
QuestionPOSTING XML Pin
Member 45955852-Jun-09 3:20
Member 45955852-Jun-09 3:20 
AnswerRe: POSTING XML Pin
Matteo Casati3-Dec-10 0:41
Matteo Casati3-Dec-10 0:41 
GeneralA minor improvement to it and it saves me a LOT of effort ;P Pin
Gr1mR33p3r7-May-09 1:43
Gr1mR33p3r7-May-09 1:43 
GeneralRe: A minor improvement to it and it saves me a LOT of effort ;P Pin
Member 45955852-Jun-09 4:12
Member 45955852-Jun-09 4:12 
GeneralRe: A minor improvement to it and it saves me a LOT of effort ;P Pin
Gr1mR33p3r2-Jun-09 18:38
Gr1mR33p3r2-Jun-09 18:38 
Make the changes as I said above and then try this:

var pl = new SOAPClientParameters();

//Build DealerInfo paramater
var dInfo = new SOAPClientParameters();
with (dInfo)
{
add("DEALER_CODE", "hjk123");
add("ID_NUMBER", "8312345678964");
}

pl.add("DEALER_INFO", dInfo.toXml());

SOAPClient.invoke(SOAP_SERVICE_URL, "helloWorld_callback", pl, true, helloWorld);
Questionproblem if proxy use in case of cross domain access Pin
nawash6-May-09 13:00
nawash6-May-09 13:00 
AnswerRe: problem if proxy use in case of cross domain access Pin
packets3-Dec-10 0:30
packets3-Dec-10 0:30 
GeneralDonate w PayPal Pin
smoore46-Mar-09 2:58
smoore46-Mar-09 2:58 
GeneralRe: Donate w PayPal Pin
Matteo Casati6-Mar-09 3:22
Matteo Casati6-Mar-09 3:22 
QuestionDoes it work with SOAP 1.2? Pin
skummy24-Nov-08 22:55
skummy24-Nov-08 22:55 
GeneralResult object is empty. Debug tips wanted. Pin
NikDaSwede9-Sep-08 8:01
NikDaSwede9-Sep-08 8:01 
GeneralUsing webservice on tomcat + axis Pin
S.Kern30-Jun-08 11:18
S.Kern30-Jun-08 11:18 
AnswerRe: Using webservice on tomcat + axis Pin
dibeonline13-Dec-08 10:45
dibeonline13-Dec-08 10:45 
GeneralBug in Soap Client version 2.1 on Safari Pin
harel gruia31-May-08 22:44
harel gruia31-May-08 22:44 
GeneralIE7 and WSO2 Pin
Sean Montague19-Mar-08 10:13
Sean Montague19-Mar-08 10:13 
GeneralProblem with Firefox Pin
cameleoni26-Oct-07 0:25
cameleoni26-Oct-07 0:25 
GeneralRe: Problem with Firefox Pin
cmumford28-May-08 8:05
cmumford28-May-08 8:05 
Generalproblems with response in EXPLORER 6.0 Pin
Lonami24-Oct-07 1:15
Lonami24-Oct-07 1:15 
GeneralAdding QueryWSInterface functionality to your client Pin
harel gruia23-Oct-07 1:07
harel gruia23-Oct-07 1:07 
QuestionSOAP call through php proxy [modified] Pin
martin-coding25-Aug-07 5:54
martin-coding25-Aug-07 5:54 
GeneralNeed help :( Pin
VjJames21-Jun-07 3:28
VjJames21-Jun-07 3:28 
QuestionHow to construct the SOAP call? Pin
JKahara12-Jun-07 2:35
JKahara12-Jun-07 2:35 

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