如何从客户端JavaScript调用Web服务？

Question

I want to call a web service of which URL is available to me. I want to just call it and retrieve the result back using javascript Ajax. For example : if some web service of like addition of two numbers is available freely and I want to use it in my app, how should I start ? I have just implemented following code (don't know it is right or not):

function webServiceCallResult(){    
    var xmlHttpReq = getXMLHttpRequest();
      if(xmlHttpReq == null){
        alert('Exception occurred');
        return false;
    }    
    var strURL = "http://www.androidpeople.com/wp-content/uploads/2010/06/example.xml";
    //var strURL = 'http://w3schools.com/dom/note.xml';
    if(xmlHttpReq.readyState == 0){
        xmlHttpReq.open('GET', strURL, true);
        xmlHttpReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        xmlHttpReq.onreadystatechange = function() {
            if (xmlHttpReq.readyState == 4) {
                var resultString = xmlHttpReq.responseXML;              
                document.getElementById('webserviceresponsetext').value = resultString.getElementsByTagName("website")[0].childNodes[0].nodeValue;  
            }
        }
        xmlHttpReq.send();
    }
}

This is working fine in IE but giving error in FF, Opera etc.like

XML parsing error,no element found Location: moz-nullprincipal:{ce91453b-f84c-4ce8-b02c-b999ef9f013a} Line Number 1, Column 1

Is it even possible to call a web service without using SOAP service request ? Thanks..

Answer 1

Unless you want to deal with the browser specific cross-compatibility stuff you should be using a library to handle Ajax requests.

Also I saw you are making an Ajax request to a different server. Unfortunately the same origin policy prevents cross domain XHR, but there is a workaround about this, by using JSONP.

I recommend using jQuery's Ajax method with JSONP, read some articles about this here: http://remysharp.com/2007/10/08/what-is-jsonp/
http://www.giantflyingsaucer.com/blog/?p=2682

Answer 2

AFAIK the same origin policy prevents cross domain XHR. You'll have to host a service on your server side which talks to the remote endpoint.

Answer 3

Are you firing the request from same domain?

Firefox won't allow you to use XMLHttpRequest to access a different domain. See the link below.

http://www.captain.at/howto-ajax-permission-denied-xmlhttprequest.php

You should call the request from the pages under http://www.androidpeople.com/ only.