A Simple AJAX DAL for use in a web app accessing a RESTful JSON API endpoints

AppDAL.js

var AppDAL = (function() {

	var _BASE_URL = "http://"+ window.location.host +"/api/";

	var _request = function(resource_uri, method, s_cback, e_cback, data) {
		data = data || null;
		var resource_url = _BASE_URL + resource_uri;

		var xhr = new window.XMLHttpRequest();
		xhr.onreadystatechange = function () {
			if ( xhr.readyState === 4 ) {
				if ( xhr.status === 200 || xhr.status === 201 || xhr.status === 202 ) {
					try {
						parsedResponse = JSON.parse(xhr.responseText);
					}
					catch (e) {
						e_cback(xhr.status, "Response Not Parsable JSON");
						return;
					}
					s_cback(parsedResponse);
				}
				else {
					e_cback(xhr.status, xhr.statusText);
				}
			}
		};
		xhr.open( method, resource_url, true );
		xhr.setRequestHeader( "Content-Type", "application/json" );

		if (data !== null) {
			xhr.send( JSON.stringify(data) );
		}
		else {
			xhr.send();
		}
	};

	return {
		get : function(resource_uri, success_cback, error_cback) {
			_request(resource_uri, "GET", success_cback, error_cback);
		},
		create : function(resource_uri, data, success_cback, error_cback) {
			_request(resource_uri, "POST", success_cback, error_cback, data);
		},
		update : function(resource_uri, data, success_cback, error_cback) {
			_request(resource_uri, "PUT", success_cback, error_cback, data);
		},
		destroy : function(resource_uri, success_cback, error_cback) {
			_request(resource_uri, "DELETE", success_cback, error_cback);
		}
	};
})();

InUse.js

(function() {

	AppDAL.get('/resource/3', function(resource) {
		// success!
	},
	function(responseCode, msg) {
		// error :(
	});

	AppDAL.update('resource/3', updated_resource, function(resource) {
		// success!
	},
	function(responseCode, msg) {
		// error :(
	});

})();