The following article is part one of a "deep dive" series on Hot Module Replacement with webpack.
module.hot API (available here)
Let's imagine for a moment it's still the middle of December and I have finished this blog post on time...
Christmas is quickly approaching and it's about time you decorate that tree in the living room. You fetch all boxes with the stuffed decoration from last year. First, you get the lights out. Make sure that you're not stressed at all while untangling them. You take a step back, maybe put on some Christmas music, make yourself a cup of tea. After a few hours, you are ready to put them on the tree. Cool, the hardest part is over. Now, you can hang some garlands and cool ornaments. Finally, you place the Star™ on the top of the tree and lit the lights. It's beautiful.
But...was that the right Star™? You decide that you actually want the shiny new rainbow Star™ instead of the conservative old yellow Star™. Do you need to remove everything and start the whole process all over just to replace that piece of decoration? Obviously not! You only need to take down the old Star™ and put the new one.
Because development with HMR is faster.
I work on the NativeScript framework and sometimes even build apps with it. Let's take a retrospective look at my life as a NativeScript developer before Hot Module Replacement:
In the video above, I'm developing an application that has a login screen and an admin screen, accessible only by authorized users. After signing in, I make a change to the admin screen. The reload process starts. We can break it down into four stages:
Now, let's see how the same process looks with Hot Module Replacement in the game:
The reload steps now are:
It is significantly faster because only the current screen is reloaded and the user session is persisted.
Webpack has three closely related terms - module, chunk, and bundle. A module is a piece of JS code that encapsulates data and provides functionality. Modules can depend on one another and thus, form a dependency graph. In the webpack bundling process, a few modules form a chunk. A bundle is an output file, produced by the bundling process. In most cases, each chunk emits exactly one bundle.
Webpack also supports a feature called hot module replacement (HMR). HMR exchanges, adds, or removes modules while an application is running, without a full reload.
However, HMR doesn't magically reload your app when you change the code. The application itself must know how to react to the incoming changes. Let's take a closer look at the HMR process.
webpack-dev-server for transferring the files. In the NativeScript ecosystem, the NativeScript CLI plays that role.
To wrap up, today we learned that:
In the next blog post in the HMR series, we'll turn our gaze to the last point. We will learn how to handle incoming changes inside our applications.