捕获mongoogse 错误信息

代码：

const mongoose = require('mongoose')

mongoose.connect('mongodb://localhost/test1', { useNewUrlParser: true })
  .then(() => console.log('数据库连接成功'))
  .catch(err => console.log('数据连接失败' + err))

// 设定集合规则
const PostSchema = new mongoose.Schema({
  title: {
    type: String,
    minlength: [4, '最小长度为4'],
    maxlength: [30, '最大长度为30'],
    trim: true,
    required: [true, '此项为必填内容']
  },
  article: {
    type: String,
    minlength: [5, '最小长度为5'],
    required: [true, '此项为必填内容']
  }
})
// 创建集合并应用规则
const Post = mongoose.model('Post', PostSchema)

Post.create({ title: '测试测试测试', article: '内容内容内容'})
.then( res => console.log(res))
.catch( err => {
  // console.log(err.errors)
  // 循环错误信息对象
  for (var attr in err.errors) {
    // 打印错误信息
    console.log('错误信息：' + err.errors[attr].message)
  }
})