v-model数据绑定分析

前端开发作者： 2024-08-21 15:55:01

v-model数据绑定分析 v-model是Vue提供的指令，其主要作用是可以实现在表单<input>、<textarea>及<s

v-model数据绑定分析

<!DOCTYPE html>
<html>
<head>
    <title>Vue</title>
</head>
<body>
    <div id="app"></div>
</body>
<script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script>
<script type="text/javascript">
    var vm = new Vue({
        el: "#app",data: {
            msg: ""
        },template: `
            <div>
                <div>Message is: {{ msg }}</div>
                <input v-model="msg">
            </div>
        `
    })
</script>
</html>

input和textarea元素使用value property和input事件。
checkbox和radio元素使用checked property和change事件。
select元素将value作为prop并将change作为事件。

<!DOCTYPE html>
<html>
<head>
    <title>Vue</title>
</head>
<body>
    <div id="app"></div>
</body>
<script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script>
<script type="text/javascript">
    var vm = new Vue({
        el: "#app",template: `
            <div>
                <div>Message is: {{ msg }}</div>
                <input :value="msg" @input="msg = $event.target.value">
            </div>
        `
    })
</script>
</html>

.trim: 输入首尾空格过滤。
.lazy: 取代input事件而监听change事件。
.number: 输入字符串转为有效的数字，如果这个值无法被parseFloat()解析，则会返回原始的值。

<!DOCTYPE html>
<html>
<head>
    <title>Vue</title>
</head>
<body>
    <div id="app"></div>
</body>
<script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script>
<script type="text/javascript">
    var vm = new Vue({
        el: "#app",data: {
            msg: 0
        },template: `
            <div>
                <div>Message is: {{ msg }}</div>
                <div>Type is: {{ typeof(msg) }}</div>
                <input v-model.number="msg" type="number">
            </div>
        `
    })
</script>
</html>

<!DOCTYPE html>
<html>
<head>
    <title>Vue</title>
</head>
<body>
    <div id="app"></div>
</body>
<script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script>
<script type="text/javascript">
    Vue.component("u-input",{
        model: {
            prop: "message",event: "input"
        },props: {
            message: { 
                type: String
            },},template: `
            <div>
                <input :value="message" @input="$emit('input',$event.target.value)">
            </div>
        `
    })
    var vm = new Vue({
        el: "#app",template: `
            <div>
                <div>Message is: {{ msg }}</div>
                <u-input v-model="msg"></u-input>
            </div>
        `
    })
</script>
</html>

// dev/src/compiler/index.js line 11
export const createCompiler = createCompilerCreator(function baseCompile (
  template: string,options: CompilerOptions
): CompiledResult {
  const ast = parse(template.trim(),options) // 生成AST
  if (options.optimize !== false) {
    optimize(ast,options) // 优化AST
  }
  const code = generate(ast,options) // 生成代码 即render字符串
  return {
    ast,render: code.render,staticRenderFns: code.staticRenderFns
  }
})

// dev/src/compiler/codegen/index.js line 43
export function generate (
  ast: ASTElement | void,options: CompilerOptions
): CodegenResult {
  const state = new CodegenState(options)
  const code = ast ? genElement(ast,state) : '_c("div")'
  return {
    render: `with(this){return ${code}}`,// render字符串
    staticRenderFns: state.staticRenderFns
  }
}

// dev/src/compiler/codegen/index.js line 55
export function genElement (el: ASTElement,state: CodegenState): string {
  // ...
  data = genData(el,state)
  // ...
}

// dev/src/compiler/codegen/index.js line 219
export function genData (el: ASTElement,state: CodegenState): string {
  // ...
  const dirs = genDirectives(el,state)
  // ...
}

// dev/src/compiler/codegen/index.js line 309
function genDirectives (el: ASTElement,state: CodegenState): string | void {
  const dirs = el.directives // 获取指令
  if (!dirs) return
  let res = 'directives:['
  let hasRuntime = false
  let i,l,dir,needRuntime
  for (i = 0,l = dirs.length; i < l; i++) { // 遍历指令
    dir = dirs[i]
    needRuntime = true
    const gen: DirectiveFunction = state.directives[dir.name] // 对于v-model来说 const gen = state.directives["model"];
    if (gen) {
      // compile-time directive that manipulates AST.
      // returns true if it also needs a runtime counterpart.
      needRuntime = !!gen(el,state.warn)
    }
    if (needRuntime) {
      hasRuntime = true
      res += `{name:"${dir.name}",rawName:"${dir.rawName}"${
        dir.value ? `,value:(${dir.value}),expression:${JSON.stringify(dir.value)}` : ''
      }${
        dir.arg ? `,arg:${dir.isDynamicArg ? dir.arg : `"${dir.arg}"`}` : ''
      }${
        dir.modifiers ? `,modifiers:${JSON.stringify(dir.modifiers)}` : ''
      }},`
    }
  }
  if (hasRuntime) {
    return res.slice(0,-1) + ']'
  }
}

// dev/src/platforms/web/compiler/directives/model.js line 14
export default function model (
  el: ASTElement,dir: ASTDirective,_warn: Function
): ?boolean {
  warn = _warn
  const value = dir.value
  const modifiers = dir.modifiers
  const tag = el.tag
  const type = el.attrsMap.type

  if (process.env.NODE_ENV !== 'production') {
    // inputs with type="file" are read only and setting the input's
    // value will throw an error.
    if (tag === 'input' && type === 'file') {
      warn(
        `<${el.tag} v-model="${value}" type="file">:\n` +
        `File inputs are read only. Use a v-on:change listener instead.`,el.rawAttrsMap['v-model']
      )
    }
  }
    
  // 分支处理
  if (el.component) {
    genComponentModel(el,value,modifiers)
    // component v-model doesn't need extra runtime
    return false
  } else if (tag === 'select') {
    genSelect(el,modifiers)
  } else if (tag === 'input' && type === 'checkbox') {
    genCheckboxModel(el,modifiers)
  } else if (tag === 'input' && type === 'radio') {
    genRadioModel(el,modifiers)
  } else if (tag === 'input' || tag === 'textarea') {
    genDefaultModel(el,modifiers)
  } else if (!config.isReservedTag(tag)) {
    genComponentModel(el,modifiers)
    // component v-model doesn't need extra runtime
    return false
  } else if (process.env.NODE_ENV !== 'production') {
    warn(
      `<${el.tag} v-model="${value}">: ` +
      `v-model is not supported on this element type. ` +
      'If you are working with contenteditable,it\'s recommended to ' +
      'wrap a library dedicated for that purpose inside a custom component.',el.rawAttrsMap['v-model']
    )
  }

  // ensure runtime directive metadata
  return true
}

// dev/src/platforms/web/compiler/directives/model.js line 127
function genDefaultModel (
  el: ASTElement,value: string,modifiers: ?ASTModifiers
): ?boolean {
  const type = el.attrsMap.type

  // warn if v-bind:value conflicts with v-model
  // except for inputs with v-bind:type
  // value与v-model冲突则发出警告
  if (process.env.NODE_ENV !== 'production') {
    const value = el.attrsMap['v-bind:value'] || el.attrsMap[':value']
    const typeBinding = el.attrsMap['v-bind:type'] || el.attrsMap[':type']
    if (value && !typeBinding) {
      const binding = el.attrsMap['v-bind:value'] ? 'v-bind:value' : ':value'
      warn(
        `${binding}="${value}" conflicts with v-model on the same element ` +
        'because the latter already expands to a value binding internally',el.rawAttrsMap[binding]
      )
    }
  }

  // 修饰符处理
  const { lazy,number,trim } = modifiers || {}
  const needCompositionGuard = !lazy && type !== 'range'
  const event = lazy
    ? 'change'
    : type === 'range'
      ? RANGE_TOKEN
      : 'input'

  let valueExpression = '$event.target.value'
  if (trim) {
    valueExpression = `$event.target.value.trim()`
  }
  if (number) {
    valueExpression = `_n(${valueExpression})`
  }

  let code = genAssignmentCode(value,valueExpression)
  if (needCompositionGuard) {
    code = `if($event.target.composing)return;${code}`
  }

  addProp(el,'value',`(${value})`)
  addHandler(el,event,code,null,true)
  if (trim || number) {
    addHandler(el,'blur','$forceUpdate()')
  }
}

// dev/src/compiler/directives/model.js line 36
export function genAssignmentCode (
  value: string,assignment: string
): string {
  const res = parseModel(value)
  if (res.key === null) {
    return `${value}=${assignment}`
  } else {
    return `$set(${res.exp},${res.key},${assignment})`
  }
}

https://github.com/WindrunnerMax/EveryDay

https://cn.vuejs.org/v2/api/#v-model
https://www.jianshu.com/p/19bb4912c62a
https://www.jianshu.com/p/0d089f770ab2
https://cn.vuejs.org/v2/guide/forms.html
https://juejin.im/post/6844903784963899400
https://juejin.im/post/6844903999414485005
https://segmentfault.com/a/1190000021516035
https://segmentfault.com/a/1190000015848976
https://github.com/haizlin/fe-interview/issues/560
https://ustbhuangyi.github.io/vue-analysis/v2/extend/v-model.html

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