import AsyncValidator from 'async-validator'
// 校验规则
const descriptor = {
 username: [
 {
  required: true,
  message: '请填写用户名'
 },
 {
  min: 3,
  max: 10,
  message: '用户名长度为3-10'
 }
 ]
}
// 根据校验规则构造一个 validator
const validator = new AsyncValidator(descriptor)
const data = {
 username: 'username'
}
validator.validate(model, (errors, fields) => {
 console.log(errors)
})

function validateData (rule, value, callback) {
 let err
 if (value === 'xxxx') {
  err = '不符合规范'
 }
 callback(err)
}
const descriptor = {
 complex: [
  {
  validator: validateData
  }
 ]
}
const validator = new AsyncValidator(descriptor)

<template>
 <form class="v-form">
  <slot></slot>
 </form> 
</template>
<script>
import AsyncValidator from 'async-validator'
export default {
 name: 'v-form',
 componentName: 'VForm', // 通过 $options.componentName 来找 form 组件
 data () {
  return {
   fields: [], // field: {prop, el}，保存 FormItem 的信息。
   formError: {}
  }
 },
 computed: {
  formRules () {
   const descriptor = {}
   this.fields.forEach(({prop}) => {
    if (!Array.isArray(this.rules[prop])) {
     console.warn(`prop 为 ${prop} 的 FormItem 校验规则不存在或者其值不是数组`)
     descriptor[prop] = [{ required: true }]
     return
    }
    descriptor[prop] = this.rules[prop]
   })
   return descriptor
  },
  formValues () {
   return this.fields.reduce((data, {prop}) => {
    data[prop] = this.model[prop]
    return data
   }, {})
  }
 },
 methods: {
  validate (callback) {
   const validator = new AsyncValidator(this.formRules)
   validator.validate(this.formValues, (errors) => {
    let formError = {}
    if (errors && errors.length) {
     errors.forEach(({message, field}) => {
      formError[field] = message
     })
    } else {
     formError = {}
    }
    this.formError = formError
    // 让错误信息的顺序与表单组件的顺序相同
    const errInfo = []
    this.fields.forEach(({prop, el}, index) => {
     if (formError[prop]) {
      errInfo.push(formError[prop])
     }
    })
    callback(errInfo)
   })
  }
 },
 props: {
  model: Object,
  rules: Object
 },
 created () {
  this.$on('form.addField', (field) => {
   if (field) {
    this.fields = [...this.fields, field]
   }
  })
  this.$on('form.removeField', (field) => {
   if (field) {
    this.fields = this.fields.filter(({prop}) => prop !== field.prop)
   }
  })
 }
}
</script>

<template>
 <div class="form-item">
  <label :for="prop" class="form-item-label" v-if="label">
   {{ label }}
  </label>
  <div class="form-item-content">
   <slot></slot>
  </div>
 </div>
</template>
<script>
export default {
 name: 'form-item',
 computed: {
  form () {
   let parent = this.$parent
   while (parent.$options.componentName !== 'VForm') {
    parent = parent.$parent
   }
   return parent
  },
  fieldError () {
   if (!this.prop) {
    return ''
   }
   const formError = this.form.formError
   return formError[this.prop] || ''
  }
 },
 props: {
  prop: String,
  label: String
 }
}
</script>

<script>
export default {
 // ...
 methods: {
  dispatchEvent (eventName, params) {
   if (typeof this.form !== 'object' && !this.form.$emit) {
    console.error('FormItem必须在Form组件内')
    return
   }
   this.form.$emit(eventName, params)
  }
 },
 mounted () {
  if (this.prop) {
   this.dispatchEvent('form.addField', {
    prop: this.prop,
    el: this.$el
   })
  }
 },
 beforeDestroy () {
  if (this.prop) {
   this.dispatchEvent('form.removeField', {
    prop: this.prop
   })
  }
 }
}
</script>

import VForm from './Form.vue'
import FormItem from './FormItem.vue'

export {
 VForm,
 FormItem
}

<template>
 <v-form :model="formData" :rules="rules" ref="form">
  <form-item label="手机号" prop="tel">
   <input type="tel" maxlength="11" v-model.trim="formData.tel"/>
  </form-item>
  <button @click="handleSubmit">保存</button>
 </v-form>
</template>
<script>
 import { VForm, FormItem } from './common/Form'
 export default {
  data () {
   return {
    formData: {
     tel: ''
    },
    rules: {
     tel: [
      {required: true, message: '您的手机号码未输入'},
      {pattern: /^1[34578]\d{9}$/, message: '您的手机号码输入错误'}
     ]
    }
   }
  },
  methods: {
   handleSubmit () {
    this.$refs.form.validate(errs => {
     console.log(errs)
    })
   }
  },
  components: {
   VForm,
   FormItem
  }
 }
</script>