{"html":"<!DOCTYPE html>\n<html>\n    <head>\n        <meta charset=utf-8>\n    </head>\n    <body>\n    \t\n        <script type=\"text/javascript\">\n            class EventEmitter {\n                // 补全代码\n                constructor() {\n                    this.eventList = {}\n                }\n\n                on(key, callback) {\n                    if(!this.eventList[key]) {\n                        this.eventList[key] = [callback]\n                    }else {\n                        this.eventList[key].push(callback)\n                    }\n                }\n\n                emit(key) {\n                    const callbacks = this.eventList[key]\n\n                    callbacks && callbacks.forEach(callback => callback())\n                }\n            }\n        </script>\n    </body>\n</html>","css":"","js":""}