Sharing code with the browser

One of the main selling points of Node.js is the fact that it's based on JavaScript and runs on V8, an engine that actually powers one of the most popular browsers: Chrome. We might think that that's enough to conclude that sharing code between Node.js and the browser is an easy task; however, as we will see, this is not always true, unless we want to share only small, self-contained, and generic fragments of code. Developing code for both the client and the server requires a non-negligible level of effort in making sure that the same code can run properly in two environments that are intrinsically different. For example, in Node.js we don't have the DOM or long-living views, while in the browser we surely don't have the filesystem or the ability to start new processes. Moreover, we need to consider that we can safely use many of the new ES2015 features in Node.js. We cannot do the same in the browser, as the majority of browsers are still stuck with ES5, and...