Static Import

The import keyword allows us to import code that has been exported by another module. By default, all modules we’re statically importing get added to the initial bundle. A module that is imported by using the default ES2015 import syntax, import module from 'module', is statically imported.

Let’s look at an example! A simple chat app contains a Chat component, in which we’re statically importing and rendering three components: UserProfile, a ChatList, and a ChatInput to type and send messages! Within the ChatInput module, we’re statically importing an EmojiPicker component to show be able to show the user the emoji picker when the user toggles the emoji.

在演练场中查看代码

The modules get executed as soon as the engine reaches the line on which we import them. When you open the console, you can see the order in which the modules have been loaded!

在演练场中查看代码

Since the components were statically imported, Webpack bundled the modules into the initial bundle. We can see the bundle that Webpack creates after building the application:

Asset           Size      Chunks            Chunk Names
main.bundle.js  1.5 MiB    main  [emitted]  main

Our chat application’s source code gets bundled into one bundle: main.bundle.js. A large bundle size can affect the loading time of our application significantly depending on the user’s device and network connection. Before the App component is able to render its contents to the user’s screen, it first has to load and parse all modules.

Luckily, there are many ways to speed up the loading time! We don’t always have to import all modules at once: maybe there are some modules that should only get rendered based on user interaction, like the EmojiPicker in this case, or rendered further down the page. Instead of importing all component statically, we can dynamically import the modules after the App component has rendered its contents and the user is able to interact with our application.