Wednesday, March 23, 2016

An Express middleware to check if a resource exists

After writing a similar code snippets for tens of times, I decided to write a middleware to handle it. The scenario is quite common. You want to check if an resource exists before going to the next step of processing. In my applications,  it is a query in the MongoDB.

 * A middleware to check if id exists in collection
 * app.get('/resources/:id/', exist('id', collection), function(req, res){...}}
 * @param  {String} id            the parameter name of item id in req object
 * @param  {Model} collection     the collection model
 * @return {Function}             the middleware
function exist(id, collection) {
  return function (req, res, next) {
    collection.findById(req.params[id]).exec(function (err, item) {
      if (err) {
        return res.send(500, 'Something wrong!');

      if (!item) {
        return res.send(404, 'item ' + req.params[id] + ' not found');
      req[req.params[id]] = item;

Introduction to REST prezi updated

I updated the prezi of an introduction to REST for next week's MSU Web Dev Cafe meeting next week. The major change was to add a case study to tell of a design is RESTful.

Tuesday, March 15, 2016

Forcing clients to reload on new application releases

Many Web application clients get data via Ajax. The resources including the CSS and JavaScript files  are never reloaded once loaded in this way. However, some new features require the clients to retrieve the updated resources from the server. This can be achieved by maintaining a service generated release number on the client, and compare that number with the current release number on the server via Ajax. If the release number is updated, then run
You will need to either disable the the cache for the resource of release number, or set cache to false of the Ajax GET request.