ESM Code Splitting Imports

[GravlLift]

Apologies if this is a very obvious question, but I couldn't find anything in the docs to explain this:

I'm looking to use esbuild to generate esm formatted output without bundling. As a simple case, I tried this.

a.ts

import { writeBLog } from "./b";
console.log("a.ts");
writeBLog();

b.ts

export function writeBLog() {
  console.log("b.js")
}

esbuild a.ts --outdir=out --format=esm

I was expecting to see both a a.js and b.js file in my out dir. Instead I only get a.js

a.js

import { writeLog } from "./b";
console.log("a.ts");
writeLog();

And of course, that import now refers to a non-existent b.js file.

It seems like esbuild is treating all files as external by default. What setting do I need to set to get esbuild to ouput a b.js file (and any other imports) as well?

EsBuild version 0.15.5

[evanw]

There’s nothing in the docs about this because this isn’t something esbuild does. You can do this by instead passing a.ts and b.ts together on the command line.

Can you say more about your use case? Why do you want to do this instead of bundling?

[GravlLift]

I'm looking to share a module in memory across multiple entry points, make use of asynchronous loading of said modules, and not duplicate code in the outputs. So in the above example, I'd like to have a third file, c.ts, that also imports b.ts. I'd list a and c and entry points, and then all three files would be output to the out directory as a.js, b.js, and c.js. Rather than duplicating the b module code in both a.js and c.js, the b module would sit in its own file.

Sounds like I'll need to declare all my files as entry points in order to accomplish what I'm trying to do? Might need to get creative with files that import a node_module...

[hyrious]

Maybe you're looking for the splitting feature.

If you want esbuild to preserve folder structure (preserveModules) #708, or manually control what files it will emit (manualChunks) #207, these are not supported yet.

[GravlLift]

Yeah, I guess #708 is indeed what I'm looking for. Thank you.