Most of the time developer need to call crm webservice or external webservice through javascript, here is the code to call crm webservice through javascript.

 var sEntityName=”nameofentity”;
 var xml = “<?xml version=”1.0″ encoding=”utf-8″?>” +
            “<soap:Envelope xmlns:soap=”http://schemas.xmlsoap.org/soap/envelope/” xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xmlns:xsd=”http://www.w3.org/2001/XMLSchema“>” + GenerateAuthenticationHeader() +
            ” <soap:Body>” +
            ” <RetrieveMultiple xmlns=”http://schemas.microsoft.com/crm/2007/WebServices“>” +
            ” <query xmlns:q1=”http://schemas.microsoft.com/crm/2006/Query” xsi:type=”q1:QueryExpression”>” +
            ” <q1:EntityName>” + sEntityName + “</q1:EntityName>” +
            ” <q1:ColumnSet xsi:type=”q1:ColumnSet”>” +
                                               //List of attributes
       ” <q1:Attributes>” +
                                                            ” <q1:Attribute>FirstAttribute</q1:Attribute>” +//In the same way you can add more attributes
                                                ” </q1:Attributes>” +
                                    ” </q1:ColumnSet>” +
                                    ” <q1:Distinct>false</q1:Distinct>” +      
                                    ” <q1:Criteria>” +
                                    ” <q1:FilterOperator>And</q1:FilterOperator>” +

     //Add conditions to your query
      ” <q1:Conditions>” +
                                                ” <q1:Condition>” +
                                                ” <q1:AttributeName>NameofAttribute</q1:AttributeName>” +
                                                ” <q1:Operator>Equal</q1:Operator>” +
                                                ” <q1:Values>” +
                                                            ” <q1:Value>”+Guid+”</q1:Value>” +
                                                ” </q1:Values>” +
                                                ” </q1:Condition>” +
                                                ” </q1:Condition>” +       
                                            ” </q1:Conditions>” +
                                    ” </q1:Criteria>” +                     
                        ” </query>” +
            ” </RetrieveMultiple>” +
            ” </soap:Body>” +
            “</soap:Envelope>”;

            //Use XMLHTTP to send request to MSCRM using the webservice CrmService.asmx
            var xmlHttpRequest = new ActiveXObject(“Msxml2.XMLHTTP”);
            xmlHttpRequest.Open(“POST”, “/mscrmservices/2007/CrmService.asmx”, false);
 
            xmlHttpRequest.setRequestHeader(“SOAPAction”,” http://schemas.microsoft.com/crm/2007/WebServices/RetrieveMultiple“);
            xmlHttpRequest.setRequestHeader(“Content-Type”, “text/xml; charset=utf-8”);
            xmlHttpRequest.setRequestHeader(“Content-Length”, xml.length);
            xmlHttpRequest.send(xml);
            //Getting the Response and Parsing
            var resultXml = xmlHttpRequest.responseXML;
            //select the node text
             alert(resultXml.selectSingleNode(“//q1:FirstAttributeName”).nodeTypedValue);
            

Hope it will help somebody.