post.json_metadata还可以按需求写入其它的数据，有点类似MongoDB。这样的话易于对文章进行过滤，也可保存一些特殊的数据。
json_metadata: "{"tags":["cn","network-institute","markdown","html"],"app":"miao","format":"markdown"}"
eg:
let jsonMetadata = {"tags": tags, "dapp": "miao", "format": "markdown", "cover": hash, "text": text}
JSON.stringify(jsonMetadata)