git bisect script for checking if flow is slow

is-flow-fast.node.mjs

#!/usr/bin/env node --experimental-modules

/* eslint-disable no-console */

import { execSync } from 'child_process';

process.env.ROOT_VIEW_PATH = `src/common/components/views/RootView.js`;

const exec = script => {
  console.log(`$ ${script}`);
  execSync(script, { stdio: 'inherit' });
};

function timeToFunFlow() {
  const startTime = Date.now();
  exec(`npm run flow`);
  const endTime = Date.now();
  const timeItTook = endTime - startTime;
  return timeItTook;
}

// execSync(`npm run flow -- stop`, { stdio: 'inherit' });

const coldStart = timeToFunFlow();
const noChanges = timeToFunFlow();

exec(`
  cat "$ROOT_VIEW_PATH" > "$ROOT_VIEW_PATH.bak"
  echo '// IGNORE THIS' >> "$ROOT_VIEW_PATH"
`);

const afterChangingAFile = timeToFunFlow();

exec(`
  cat "$ROOT_VIEW_PATH.bak" > "$ROOT_VIEW_PATH"
  rm "$ROOT_VIEW_PATH.bak"
`);

console.log(`Time it took to run flow:`, {
  coldStart,
  noChanges,
  afterChangingAFile
});

if (afterChangingAFile > 30000) {
  throw new Error(`expected flow to be fast, but it wasn't`);
}

./scripts/flow-is-fast.node.mjs && echo 'win' || echo 'fail'

Only weird thing (so far!) about using the #!/usr/bin/env node --experimental-modules trick is that __dirname doesn't exist.
weird! But not weird enough to waste time figuring out why 🤷‍♂️