Overleaf/services/clsi/app/js/DraftModeManager.js

import fsPromises from 'node:fs/promises'
import { callbackify } from 'node:util'
import logger from '@overleaf/logger'

const PREFIX =
  '\\PassOptionsToPackage{draft}{graphicx}\\PassOptionsToPackage{draft}{graphics}'

async function injectDraftMode(filename) {
  const content = await fsPromises.readFile(filename, { encoding: 'utf8' })
  const modifiedContent = PREFIX + content
  logger.debug(
    {
      content: content.slice(0, 1024), // \documentclass is normally v near the top
      modifiedContent: modifiedContent.slice(0, 1024),
      filename,
    },
    'injected draft class'
  )
  await fsPromises.writeFile(filename, modifiedContent, { encoding: 'utf8' })
}

export default {
  PREFIX,
  injectDraftMode: callbackify(injectDraftMode),
  promises: { injectDraftMode },
}