发贴或评论都是用的同一个函数，只是评论的parent_author为空。

steem.broadcast.comment(wif, parentAuthor, parentPermlink, author, permlink, title, body, jsonMetadata, function(err, result) {
  console.log(err, result)
})

//函数讲解
steem.broadcast.comment (
    wif,                 //发帖密钥
    parentAuthor,        // 如果是发帖则为空，如果是评论则为父帖作者
    parentPermlink,      // 如果是发帖则为主标签，如果是评论则为父帖地址
    author,              // 作者
    permlink,            // URL地址
    title,               // 标题
    body,                // 内容
    jsonMetadata         // json
)

eg:
let wif = '5pfffff'
let parentAuthor = ''
let parentPermlink = 'cn'
let author = 'lemooljiang'
let permlink = 'kdk54gf'
let title = '这是标题'
let body = '这是正文' 
let tags = ['cn', 'starnote', 'bitcoin']
let jsonMetadata = {"tags": tags, "dapp": "moochain", "format": "markdown", "cover": hash, "text": text}

this.steem.broadcast.comment(wif, parentAuthor, parentPermlink, author, permlink, title, body, jsonMetadata, function(err, result) {
  console.log(1234, err, result);
  })