Instead of using XRM WebAPI JS using XML HTTP for sync calls sample code

 function createPrescription(formContext)
{
	
	var currentDAID =  formContext.data.entity.getId();
    currentDAID = currentDAID.replace("{","").replace("}","");
	var count = GetCountofExisitingPrescriptions(currentDAID);
	alert(count);
	if(count<=0)
	{
	var data =
    {
        "lifeline_name": "Prescription",
		"lifeline_issuedate" : new Date(),
		"lifeline_DoctorAppointment@odata.bind": "lifeline_doctorappointments("+currentDAID+")"	
    }
    Xrm.WebApi.createRecord("lifeline_prescription", data).then(
		function success(result) {
		 alert("Prescription created successfully.");
		},
		function (error) {
			console.log(error.message);
			// handle error conditions
		}
	);	
	}
	else{
		alert("Aleady prescription crerated.");
	}
}

function GetCountofExisitingPrescriptions(docappid)
{
	//debugger;
	var fetchXml = "<fetch version='1.0' output-format='xml-platform' mapping='logical' distinct='false'>"+
		"  <entity name='lifeline_prescription'>"+
		"    <attribute name='lifeline_prescriptionid' />"+
		"    <attribute name='lifeline_name' />"+
		"    <attribute name='createdon' />"+
		"    <order attribute='lifeline_name' descending='false' />"+
		"    <filter type='and'>"+
		"      <condition attribute='lifeline_doctorappointment' operator='eq' uitype='lifeline_doctorappointment' value='{"+docappid+"}' />"+
		"    </filter>"+
		"  </entity>"+
		"</fetch>"
    var encodedFetchXML = encodeURI(fetchXml);
	var query = "/api/data/v9.2/lifeline_prescriptions?fetchXml="+encodedFetchXML;
	var globalContext = Xrm.Utility.getGlobalContext();
	var finalpathwithquery = globalContext.getClientUrl() + query;
	
	
	//use XML HTTP Request for webAPI call
	var data = null;
	var isAsync = false;

	var req = null;
	if (window.XMLHttpRequest) {
		req = new XMLHttpRequest();
	} 
	else if (window.ActiveXObject) {
		req = new ActiveXObject("MSXML2.XMLHTTP.3.0");
	}

	req.open("GET",finalpathwithquery,isAsync);
	req.setRequestHeader("OData-MaxVersion", "4.0");
	req.setRequestHeader("OData-Version", "4.0");
	req.setRequestHeader("Accept", "application/json");
	req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
	req.setRequestHeader("Prefer", "odata.include-annotations=\"*\"");
	
	req.onreadystatechange = function () {
		if (this.readyState === 4) {
			req.onreadystatechange = null;
			if (this.status === 200) {
				var result = JSON.parse(this.response);
				data = result;
			} 
			else {
				Xrm.Utility.alertDialog(this.statusText);
			}
		}
	};
	req.send();
		
	return data.value.length;
}