title: rollup.js: How to disable output?
body: <p>I'm trying to use the rollup JS API. <a href="https://rollupjs.org/guide/en/#rolluprollup" rel="nofollow noreferrer">rollup.rollup</a> doesn't require me to specify the <code>output</code> option but it appears <a href="https://rollupjs.org/guide/en/#rollupwatch" rel="nofollow noreferrer">rollup.watch</a> does for some reason.</p>
  
  <p>Here's what I've got:</p>
  
  <pre><code>#!/usr/bin/env node
  import * as rollup from 'rollup';
  
  async function main() {
      const watcher = rollup.watch({
          input: 'src/main.ts',
          // output: {
          //     dir: 'dist'
          // }
      })
  
      watcher.on('event', event =&gt; {
          console.log(event);
      })
  }
  
  
  main().catch(err =&gt; {
      console.error(err);
      process.exit(1);
  })
  </code></pre>
  
  <p>It's saying:</p>
  
  <pre><code>{
    code: 'ERROR',
    error: Error: You must specify "output.file" or "output.dir" for the build.
        at error (file:///somepath/screeps/node_modules/rollup/dist/es/shared/rollup.js:10380:30
  )
        at Object.write (file:///somepath/screeps/node_modules/rollup/dist/es/shared/rollup.js:1
  8594:24)
        at file:///somepath/screeps/node_modules/rollup/dist/es/shared/watch.js:7083:86
        at Array.map (&lt;anonymous&gt;)
        at Task.run (file:///somepath/screeps/node_modules/rollup/dist/es/shared/watch.js:7083:6
  3)
        at async Watcher.run (file:///somepath/screeps/node_modules/rollup/dist/es/shared/watch.
  js:7003:17) {
      code: 'MISSING_OPTION'
    }
  }
  </code></pre>
  
  <p>I should be able to get what I need out of the event emitter though -- I don't want to write it to disk. How do I disable that?</p>