JavaScript Callbacks

If you need to access the response from an asynchronous XMLHttpRequest, provide your request with a callback. The code below retrieves a Contact from CRM by its ID. In the success function, a callback is called, passing it the result from the request (which should be the Contact).

	function getContact(id, callback) {
	$.ajax({
	type: "GET",
	contentType: "application/json; charset=utf-8",
	datatype: "json",
	url: Xrm.Page.context.getClientUrl() + "/XRMServices/2011/OrganizationData.svc/ContactSet(guid'" + contactId + "')",
	beforeSend: function (XMLHttpRequest) { XMLHttpRequest.setRequestHeader("Accept", "application/json"); },
	async: true,
	success: function (data, textStatus, xhr) {
	callback(data.d);
	},
	error: function (xhr, textStatus, errorThrown) {
	console.error(errorThrown);
	}
	});
	}

view raw getContact.js hosted with ❤ by GitHub

To make use of the result, create a function to call getContact, and evaluate its result:

	function sayHelloIfNameIsDave() {
	var contactId = Xrm.Page.getAttribute("customerid").getValue()[0].id;
	getContact(contactId, function(contact) {
	if (contact.Firstname === "Dave")
	alert("Hello");
	});
	}

view raw sayHello.js hosted with ❤ by GitHub

The callback is called once the response is ready. Notice that the callback function is passed anonymously here as the second parameter of the call to getContact. It is advisable to write this anonymous function separately and give it a name.