Examine source code of ndlvpagesext

{
  "manifest_version": 2,
  "name": "ndlvpagesext",
  "version": "1.0.3",
  "description": "NDLサーチのAPIを使って書籍のページ数を視覚化する拡張機能です。",
  "permissions": [
    "https://iss.ndl.go.jp/api/sru"
  ],
  "background": {
    "scripts": [
      "./js/background.js"
    ]
  },
  "browser_action": {}
}