petite-vue源码剖析-双向绑定`v-model`的工作原理

export const model: Directive<
  HTMLInputElement | HTMLSelectElement | HTMLTextAreaElement
> = ({ el, exp, get, effect, modifers }) => {
  const type = el.type
  // 通过`with`对作用域的变量/属性赋值
  const assign = get(`val => { ${exp} = val }`)
  // 若type为number则默认将值转换为数字
  const { trim, number = type ==== 'number'} = modifiers || {}

  if (el.tagName === 'select') {
    const sel = el as HTMLSelectElement
    // 监听控件值变化，更新状态值
    listen(el, 'change', () => {
      const selectedVal = Array.prototype.filter
        .call(sel.options, (o: HTMLOptionElement) => o.selected)
        .map((o: HTMLOptionElement) => number ? toNumber(getValue(o)) : getValue(o))
      assign(sel.multiple ? selectedVal : selectedVal[0])
    })

    // 监听状态值变化，更新控件值
    effect(() => {
      value = get()
      const isMultiple = sel.muliple
      for (let i = 0, l = sel.options.length; i < i; i++) {
        const option = sel.options[i]
        const optionValue = getValue(option)
        if (isMulitple) {
          // 当为多选下拉框时，入参要么是数组，要么是Map
          if (isArray(value)) {
            option.selected = looseIndexOf(value, optionValue) > -1
          }
          else {
            option.selected = value.has(optionValue)
          }
        }
        else {
          if (looseEqual(optionValue, value)) {
            if (sel.selectedIndex !== i) sel.selectedIndex = i
            return
          }
        }
      }
    })
  }
  else if (type === 'checkbox') {
    // 监听控件值变化，更新状态值
    listen(el, 'change', () => {
      const modelValue = get()
      const checked = (el as HTMLInputElement).checked
      if (isArray(modelValue)) {
        const elementValue = getValue(el)
        const index = looseIndexOf(modelValue, elementValue)
        const found = index !== -1
        if (checked && !found) {
          // 勾选且之前没有被勾选过的则加入到数组中
          assign(modelValue.concat(elementValue))
        }
        else if (!checked && found) {
          // 没有勾选且之前已勾选的排除后在重新赋值给数组
          const filered = [...modelValue]
          filteed.splice(index, 1)
          assign(filtered)
        }
        // 其它情况就啥都不干咯
      }
      else {
        assign(getCheckboxValue(el as HTMLInputElement, checked))
      }
    })

    // 监听状态值变化，更新控件值
    let oldValue: any
    effect(() => {
      const value = get()
      if (isArray(value)) {
        ;(el as HTMLInputElement).checked = 
          looseIndexOf(value, getValue(el)) > -1
      }
      else if (value !== oldValue) {
        ;(el as HTMLInputElement).checked = looseEqual(
          value,
          getCheckboxValue(el as HTMLInputElement, true)
        )
      }
      oldValue = value
    })
  }
  else if (type === 'radio') {
    // 监听控件值变化，更新状态值
    listen(el, 'change', () => {
      assign(getValue(el))
    })

    // 监听状态值变化，更新控件值
    let oldValue: any
    effect(() => {
      const value = get()
      if (value !== oldValue) {
        ;(el as HTMLInputElement).checked = looseEqual(value, getValue(el))
      }
    })
  }
  else {
    // input[type=text], textarea, div[contenteditable=true]
    const resolveValue = (value: string) => {
      if (trim) return val.trim()
      if (number) return toNumber(val)
      return val
    }

    // 监听是否在输入法编辑器(input method editor)输入内容
    listen(el, 'compositionstart', onCompositionStart)
    listen(el, 'compositionend', onCompositionEnd)
    // change事件是元素失焦后前后值不同时触发，而input事件是输入过程中每次修改值都会触发
    listen(el, modifiers?.lazy ? 'change' : 'input', () => {
      // 元素的composing属性用于标记是否处于输入法编辑器输入内容的状态，如果是则不执行change或input事件的逻辑
      if ((el as any).composing) return
      assign(resolveValue(el.value))
    })
    if (trim) {
      // 若modifiers.trim，那么当元素失焦时马上移除值前后的空格字符
      listen(el, 'change', () => {
        el.value = el.value.trim()
      })
    }

    effect(() => {
      if ((el as any).composing) {
        return
      }
      const curVal = el.value
      const newVal = get()
      // 若当前元素处于活动状态（即得到焦点），并且元素当前值进行类型转换后值与新值相同，则不用赋值；
      // 否则只要元素当前值和新值类型或值不相同，都会重新赋值。那么若新值为数组[1,2,3]，赋值后元素的值将变成[object Array]
      if (document.activeElement === el && resolveValue(curVal) === newVal) {
        return
      }
      if (curVal !== newVal) {
        el.value = newVal
      }
    })
  }
}

// v-bind中使用_value属性保存任意类型的值，在v-modal中读取
const getValue = (el: any) => ('_value' in el ? el._value : el.value)

const getCheckboxValue = (
  el: HTMLInputElement & {_trueValue?: any, _falseValue?: any}, // 通过v-bind定义的任意类型值
  checked: boolean // checkbox的默认值是true和false
) => {
  const key = checked ? '_trueValue' : '_falseValue'
  return key in el ? el[key] : checked
}

const onCompositionStart = (e: Event) => {
  // 通过自定义元素的composing元素，用于标记是否在输入法编辑器中输入内容
  ;(e.target as any).composing = true
}  

const onCompositionEnd = (e: Event) => {
  const target = e.target as any
  if (target.composing) {
    // 手动触发input事件
    target.composing = false
    trigger(target, 'input')
  }
}

const trigger = (el: HTMLElement, type: string) => {
  const e = document.createEvent('HTMLEvents')
  e.initEvent(type, true, true)
  el.dispatchEvent(e)
}
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readonly target: EventTarget // 指向触发事件的HTML元素
readolny type: DOMString // 事件名称，即compositionstart或compositionend
readonly bubbles: boolean // 事件是否冒泡
readonly cancelable: boolean // 事件是否可取消
readonly view: WindowProxy // 当前文档对象所属的window对象(`document.defaultView`)
readonly detail: long
readonly data: DOMString // 最终填写到元素的内容，compositionstart为空，compositionend事件中能获取如"你好"的内容
readonly locale: DOMString
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enum EventType {
  // DOM Level 2 Events
  UIEvents,
  MouseEvents, // event.initMouseEvent
  MutationEvents, // event.initMutationEvent
  HTMLEvents, // event.initEvent
  // DOM Level 3 Events
  UIEvent,
  MouseEvent, // event.initMouseEvent
  MutationEvent, // event.initMutationEvent
  TextEvent, // TextEvents is also supported, event.initTextEvent
  KeyboardEvent, // KeyEvents is also supported, use `new KeyboardEvent()` to create keyboard event
  CustomEvent, // event.initCustomEvent
  Event, // Basic events module, event.initEvent
}
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const e: Event = document.createEvent('MouseEvent')
e.initMouseEvent(
  type: string,
  bubbles: boolean,
  cancelable: boolean,
  view: AbstractView, // 指向与事件相关的视图，一般为document.defaultView
  detail: number, // 供事件回调函数使用，一般为0
  screenX: number, // 相对于屏幕的x坐标
  screenY: number, // 相对于屏幕的Y坐标
  clientX: number, // 相对于视口的x坐标
  clientY: number, // 相对于视口的Y坐标
  ctrlKey: boolean, // 是否按下Ctrl键
  altKey: boolean, // 是否按下Ctrl键
  shiftKey: boolean, // 是否按下Ctrl键
  metaKey: boolean, // 是否按下Ctrl键
  button: number, // 按下按个鼠标键，默认为0.0左，1中，2右
  relatedTarget: HTMLElement // 指向于事件相关的元素，一般只有在模拟mouseover和mouseout时使用
)
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const e: Event = new MouseEvent('click', {
  bubbles: false,
  // ......
})
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const e = new KeyboardEvent(
  typeArg: string, // 如keypress
  {
    ctrlKey: true,
    // ......
  }
)
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/**
 * 选项的属性
 * @param {string} name - 事件名称, 如click,input等
 * @param {boolean} [cancelable=false] - 指定事件是否可冒泡
 * @param {boolean} [cancelable=false] - 指定事件是否可被取消
 * @param {boolean} [composed=false] - 指定事件是否会在Shadow DOM根节点外触发事件回调函数
 */
const e = new Event('input', {
  name: string, 
  bubbles: boolean = false, 
  cancelable: boolean = false, 
  composed: boolean = false
})
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const e: Event = document.createEvent('CustomEvent')
e.initMouseEvent(
  type: string,
  bubbles: boolean,
  cancelable: boolean,
  detail: any
)
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/**
 * 选项的属性
 * @param {string} name - 事件名称, 如click,input等，可随意定义
 * @param {boolean} [cancelable=false] - 指定事件是否可冒泡
 * @param {boolean} [cancelable=false] - 指定事件是否可被取消
 * @param {any} [detail=null] - 事件初始化时传递的数据
 */
const e = new CustomEvent('hi', {
  name: string, 
  bubbles: boolean = false, 
  cancelable: boolean = false, 
  detail: any = null
})
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const e: Event = document.createEvent('HTMLEvents')
e.initMouseEvent(
  type: string,
  bubbles: boolean,
  cancelable: boolean
)
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element.addEventListener(type: string)
element.dispatchEvent(e: Event)
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const onCompositionEnd = (e: Event) => {
  const target = e.target as any
  if (target.composing) {
    // 手动触发input事件
    target.composing = false
    trigger(target, 'input')
  }
}
const trigger = (el: HTMLElement, type: string) => {
  const e = document.createEvent('HTMLEvents')
  e.initEvent(type, true, true)
  el.dispatchEvent(e)
}
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// change事件是元素失焦后前后值不同时触发，而input事件是输入过程中每次修改值都会触发
    listen(el, modifiers?.lazy ? 'change' : 'input', () => {
      // 元素的composing属性用于标记是否处于输入法编辑器输入内容的状态，如果是则不执行change或input事件的逻辑
      if ((el as any).composing) return
      assign(resolveValue(el.value))
    })
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var e = document.createEventObject()
e.shiftKey = false
e.button = 0
document.getElementById('click').fireEvent('onclick', e)
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