The import statement returns a promise, so you can lazily load modules as required (i.e. don't load everything up front, only load on-demand as users are using your app).

You don't need to complicate things - just use vanilla JavaScript features as they were intended.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guid...

In practice, you are likely to have to contort your code very significantly to use dynamic imports pervasively. And pervasive usage such as you seem to be describing is emphatically not how dynamic imports were intended to be used, and wouldn’t speed things up much in general anyway (because you still can’t do anything until your dependencies have loaded), and stands a good chance of being slower.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... expresses it well:

> Use dynamic import only when necessary. The static form is preferable for loading initial dependencies, and can benefit more readily from static analysis tools and tree shaking.

(Also, a quibble over your wording: dynamic imports aren’t a statement, but a call, though not a function call.)

You need to develop with this in mind from the start. I am not suggesting refactoring an existing application to use it for every single dependency as yes that would be a pain.

Instead import your initial generic dependencies up-front as usual, but then notionally break your application up by CUJ and load the CUJ-specific code dynamically as needed.

E.g. for a hypothetical email client you would import the initial "inbox view" code upfront (along with generic common dependencies), but you might not import the code needed for a rich text editor until the user clicks on the "write email" button, saving that network load and code execution for when - or indeed if - the user actually needs it.

Given the context (waterfall stuff), I was assuming you were describing pervasive dynamic imports, since the selective use of dynamic imports for code splitting is fairly standard practice. (And indeed, I know from working on it a few years back and doing most of the porting from a custom module system to ECMAScript modules, Fastmail’s webmail works in this way, though my recollection is that compose specifically is preloaded once the rest of the mail stuff is done, so that when you hit that compose button it’s almost certainly ready to go common fault of code splitting is deferring loading too long, so that you end up slowing users down.)

When I spoke of unused code, I was meaning things like a file containing a bunch of functions, of which you only use one, and so there are the other functions and perhaps deeper imports that weren’t actually necessary; a bundler would remove all the unused stuff. The “solution” in such a case would be to do something like splitting each function into its own file, but that’s worse than before because now your import chains are probably even longer, and even more files have to be loaded (and there is still some filewise overhead, even if HTTP/2 improves it drastically).

I’ll temper my expressed position slightly by saying that bundling is not so significantly advantageous if you have written all of the code (you’re not importing third-party libraries), and keep your file count fairly low and import depth very low. But at that point, perhaps you should have just dropped it all in one file.

Don’t use external dependencies (:D), don’t write code you don’t use, encapsulate imports in custom elements (this is a joke).

Without any runtime boilerplate like module bundling, corejs polyfills and the usual frontend/css-in-js frameworks, all code that gets downloaded is your code, so make it count. 640 kilobytes should be enough for everyone.

For runtime boilerplate: yeah, don’t use webpack, it does indeed add silly boilerplate (and structures things in a way that almost requires source map tooling to understand!); use Rollup instead, which pretty much writes just what you would have written if you had put everything in one file, with no overhead whatsoever. (If you happen not to be familiar with it, take a look at the examples in https://www.rollupjs.org/repl/.) Also ditch core-js as it’s almost certainly unnecessary if ES modules are your baseline.

But even if you’re not using external dependencies, I maintain: by not bundling, you’re slowing things down, and it’s generally the people on the other side of the world from your servers and the disadvantaged with less-powerful computers and more expensive data that will suffer for your whim.

From what I’ve seen, many built-and-bundled apps have run into security issues in dependencies and have been forced to switch to ESM versions which are highly incompatible with CJS-targeting builds and so require significant retooling just to fix trivial security issues.

It’s not npm’s fault for sure, but the ecosystem is fundamentally divergent on this issue and there doesn’t seem to be a universal solution.

I’m confused by your comment, because it doesn’t seem relevant and I don’t understand what you’re saying. My first impression is that you seem to be implying that the security issues in dependencies are in some way linked to the module format (ES/CommonJS), which is not the case. I can’t see why such issues would force a switch in either direction for anyone, given especially that ESM bundlers can generally slurp ECMAScript Modules and CommonJS alike (e.g. Rollup via @rollup/plugin-commonjs) with only rare compatibility issues after at most a little configuration, generally associated with very-badly-written code. Given how much of the npm ecosystem is still on CommonJS modules, there’d be much more outcry if you could’t intermingle the two in a bundler. So if what you had in mind was something like “version x was CommonJS and has a bug, version y is ESM and has fixed the bug”, well, you can probably update to y easily (at least as far as the CommonJS/ESM divide is concerned), and if you were forking or anything, if the bug is clearly identified then patching it onto x is easy too.

In practice, there are packages which have moved on to ESM and which no longer maintain their CJS version (at least as actively), making life difficult for maintainers of projects dependent on those CJS packages with published vulnerabilities.

A CJS-targeting build can’t slurp up ESM dependencies. Not without dubious hacks, at least.

See e.g. https://stackoverflow.com/questions/70545129/compile-a-packa...