markdown-viewer/js/background/background.js

// chrome.storage.sync.clear()
chrome.storage.sync.get(function (sync) {
  if (!sync.options)
    chrome.storage.sync.set({options: md.defaults})
  if (!sync.theme)
    chrome.storage.sync.set({theme: 'github'})
  if (sync.raw === undefined)
    chrome.storage.sync.set({raw: false})
})

chrome.tabs.onUpdated.addListener(function (id, info, tab) {
  if (info.status === 'complete') return
  if (/.*\/.*\.(?:markdown|mdown|mkdn|md|mkd|mdwn|mdtxt|mdtext|text)(?:#.*)?$/
    .test(tab.url)) {
    chrome.pageAction.show(id)
  }
})

chrome.extension.onMessage.addListener(function (req, sender, sendResponse) {
  switch (req.message) {
    case 'markdown':
      md.compile(req.markdown, sendResponse)
      break

    case 'settings':
      chrome.storage.sync.get(['options', 'theme', 'raw'], function (data) {
        delete data.options.langPrefix
        sendResponse(data)
      })
      break

    case 'options':
      req.options.langPrefix = 'language-'//prism
      chrome.storage.sync.set({options: req.options}, sendResponse)
      sendMessage({message: 'reload'})
      break
    case 'defaults':
      chrome.storage.sync.set({options: md.defaults}, sendResponse)
      chrome.storage.sync.set({theme: 'github'})
      chrome.storage.sync.set({raw: false})
      sendMessage({message: 'reload'})
      break

    case 'theme':
      chrome.storage.sync.set({theme: req.theme}, sendResponse)
      sendMessage({message: 'theme', theme: req.theme})
      break

    case 'raw':
      chrome.storage.sync.set({raw: req.raw}, sendResponse)
      sendMessage({message: 'raw'})
      break
  }
  return true
})

function sendMessage (obj) {
  chrome.tabs.query({active: true, currentWindow: true}, function (tabs) {
    chrome.tabs.sendMessage(tabs[0].id, obj)
  })
}