有时为了方便调试，我们需要手动模拟一个json 字符串常量。例如： let jsonStr = "{"citys":[{"id": 9,"code":"100000","name":"北京市","baiduCode":"131","gaodeCode":"","tengxunCode":"","parentId":8,"level": 2,"areas":[{"id":10,"code":"100020","name":"朝阳区","baiduCode":"","gaodeCode": "","tengxunCode":"","parentId":9,"level":3,"areas": 50},{"id":13,"code":"100089","name":"海淀区","baiduCode":60,"gaodeCode":20,"tengxunCode":10,"parentId":9,"level": 3,"areas": 90}]},{"id": 12,"code": "300000","name":"天津市","baiduCode":80,"gaodeCode":80,"tengxunCode":30,"parentId":11,"level":2,"areas":60}]}"
