book.json

{
    "plugins": [ "addcssjs", "edit-link", "theme-api", "jsfiddle", "custom-favicon", "simple-page-toc", "anchors"  ],
    "pluginsConfig": {
        "edit-link": {
            "base": "https://github.com/i18next/i18next-gitbook/edit/master/",
            "label": "Edit"
        },
        "theme-api": {
            "languages": [
                {
                    "lang": "js",
                    "name": "js",
                    "default": true
                }
            ],
            "split": true
        },
        "jsfiddle":{
            "type": "script",
            "tabs": ["result","js"],
            "height": "500",
            "width": "500"
        },
        "favicon": "assets/favicon.ico",
        "simple-page-toc": {
            "maxDepth": 3,
            "skipFirstH1": true
       },
       "addcssjs": {
         "js": ["assets/js/custom.js"]
      }
    }
}