How to remove comments when building TypeScript into JavaScripts using rollup

You should be able to achieve this too with just rollup-plugin-terser. It bases on terser so more information it's actually available on its README, here is the part related to minification. So in your case this part of rollup.config.js should looks like:

plugins: [
  terser({
// remove all comments
    format: {
      comments: false
    },
// prevent any compression
    compress: false
  }),
],

Keep in mind, that you can also enable part of configuration for production only. So having declared production const in your rollup.config.js you can do like that:

import { terser } from 'rollup-plugin-terser';

const production = !process.env.ROLLUP_WATCH;

export default {
  plugins: [
    production && terser({
      // terser plugin config here
    }),
  ],
};

Like @jujubes answered in the comments, the rollup-plugin-cleanup will do the task. I want to expand a bit.

Three things:

• Add ts to extensions list, like extensions: ["js", "ts"] — otherwise sources won't be processed, even if transpiling step typescript() is before it — I originally came here investigating why rollup-plugin-cleanup won't work on TS files and it was just ts extension missing ‍♂️
• code coverage is important; on default settings, this plugin would remove istanbul statements like /* istanbul ignore else */ so it's good to exclude them, comments: "istanbul",
• removing console.log is a separate challenge which is done with @rollup/plugin-strip and it goes in tandem to rollup-plugin-cleanup. In my case, depending is it a "dev" or "prod" Rollup build (controlled by a CLI flag --dev, as in rollup -c --dev), I remove console.log on prod builds only. But comments are removed on both dev and prod builds.

currently, I use:

import cleanup from "rollup-plugin-cleanup";
...
{
  input: "src/main.ts",
  output: ...,
  external: ...,
  plugins: [
    ...
    cleanup({ comments: "istanbul", extensions: ["js", "ts"] }),
    ...

Here's an example of rollup-plugin-cleanup being used my Rollup config, here's my Rollup config generator (in monorepos, Rollup configs are hard to maintain by hand so I generate them). If you decide to wire up --dev CLI flag, the gotcha is you have to remove the flag from the commandLineArgs before script ends, otherwise Rollup will throw, see the original tip and it in action.