指令

编译型指令

在编译时处理的指令主要有v-once、v-if和v-for

import("../vue.study.esm.js").then((module) => {
  const { Vue } = module;

  const o = Vue.compile("<span v-once>test</span>");

  const i = Vue.compile('<span v-if="true">test</span>');

  const f = Vue.compile('<span v-for="item in [2, 4, 6]">test</span>');

  const oi = Vue.compile('<span v-once v-if="true">test</span>');
});

核心代码为/src/compiler/index.ts，通过断点调试可知。v-once被解析为抽象语法树节点的属性once，v-if指令被解析为属性if和ifConditions，生成渲染函数代码时为

export const createCompiler = createCompilerCreator(function baseCompile(
  template: string,
  options: CompilerOptions
): CompiledResult {
  const ast = parse(template.trim(), options)
  if (options.optimize !== false) {
    optimize(ast, options)
  }
  const code = generate(ast, options)
  return {
    ast,
    render: code.render,
    staticRenderFns: code.staticRenderFns,
  }
})

生成渲染代码的核心代码在src/compiler/codegen/index.ts的genElement，这里可以看到v-once、v-for、v-if依次处理。v-once按情况被处理为***?_m():***、_m()、_o等，v-for被处理为_l()，v-if被处理成三元运算表达式的样子。

export function genElement(el: ASTElement, state: CodegenState): string {
  if (el.parent) {
    el.pre = el.pre || el.parent.pre
  }

  if (el.staticRoot && !el.staticProcessed) {
    return genStatic(el, state)
  } else if (el.once && !el.onceProcessed) {
    return genOnce(el, state)
  } else if (el.for && !el.forProcessed) {
    return genFor(el, state)
  } else if (el.if && !el.ifProcessed) {
    return genIf(el, state)
  } else if (el.tag === 'template' && !el.slotTarget && !state.pre) {
    return genChildren(el, state) || 'void 0'
  } else if (el.tag === 'slot') {
    return genSlot(el, state)
  } else {
    // component or element
    let code
    if (el.component) {
      code = genComponent(el.component, el, state)
    } else {
      let data
      if (!el.plain || (el.pre && state.maybeComponent(el))) {
        data = genData(el, state)
      }

      const children = el.inlineTemplate ? null : genChildren(el, state, true)
      code = `_c('${el.tag}'${
        data ? `,${data}` : '' // data
      }${
        children ? `,${children}` : '' // children
      })`
    }
    // module transforms
    for (let i = 0; i < state.transforms.length; i++) {
      code = state.transforms[i](el, code)
    }
    return code
  }
}

function genOnce(el: ASTElement, state: CodegenState): string {
  el.onceProcessed = true
  if (el.if && !el.ifProcessed) {
    return genIf(el, state)
  } else if (el.staticInFor) {
    let key = ''
    let parent = el.parent
    while (parent) {
      if (parent.for) {
        key = parent.key!
        break
      }
      parent = parent.parent
    }
    if (!key) {
      process.env.NODE_ENV !== 'production' &&
        state.warn(
          `v-once can only be used inside v-for that is keyed. `,
          el.rawAttrsMap['v-once']
        )
      return genElement(el, state)
    }
    return `_o(${genElement(el, state)},${state.onceId++},${key})`
  } else {
    return genStatic(el, state)
  }
}

export function genFor(
  el: any,
  state: CodegenState,
  altGen?: Function,
  altHelper?: string
): string {
  const exp = el.for
  const alias = el.alias
  const iterator1 = el.iterator1 ? `,${el.iterator1}` : ''
  const iterator2 = el.iterator2 ? `,${el.iterator2}` : ''

  if (
    process.env.NODE_ENV !== 'production' &&
    state.maybeComponent(el) &&
    el.tag !== 'slot' &&
    el.tag !== 'template' &&
    !el.key
  ) {
    state.warn(
      `<${el.tag} v-for="${alias} in ${exp}">: component lists rendered with ` +
        `v-for should have explicit keys. ` +
        `See https://vuejs.org/guide/list.html#key for more info.`,
      el.rawAttrsMap['v-for'],
      true /* tip */
    )
  }

  el.forProcessed = true // avoid recursion
  return (
    `${altHelper || '_l'}((${exp}),` +
    `function(${alias}${iterator1}${iterator2}){` +
    `return ${(altGen || genElement)(el, state)}` +
    '})'
  )
}

function genIfConditions(
  conditions: ASTIfConditions,
  state: CodegenState,
  altGen?: Function,
  altEmpty?: string
): string {
  if (!conditions.length) {
    return altEmpty || '_e()'
  }

  const condition = conditions.shift()!
  if (condition.exp) {
    return `(${condition.exp})?${genTernaryExp(
      condition.block
    )}:${genIfConditions(conditions, state, altGen, altEmpty)}`
  } else {
    return `${genTernaryExp(condition.block)}`
  }

  // v-if with v-once should generate code like (a)?_m(0):_m(1)
  function genTernaryExp(el) {
    return altGen
      ? altGen(el, state)
      : el.once
      ? genOnce(el, state)
      : genElement(el, state)
  }
}

v-on

v-on用于绑定事件

import("../vue.study.esm.js").then((module) => {
  const { Vue } = module;

  const app = new Vue({
    data() {
      return {
        value: 1,
      };
    },
    template: "<span v-on:click='value++'>{{value}}</span>"
  });
  app.$mount("#app");
});

在解析AST时处理标签结尾时调用closeElement->processElement->processAttrs->addHandler会对v-on解析为events属性。

function processAttrs(el) {
  const list = el.attrsList
  let i, l, name, rawName, value, modifiers, syncGen, isDynamic
  for (i = 0, l = list.length; i < l; i++) {
    name = rawName = list[i].name
    value = list[i].value
    if (dirRE.test(name)) {
      // mark element as dynamic
      el.hasBindings = true
      // modifiers
      modifiers = parseModifiers(name.replace(dirRE, ''))
      // support .foo shorthand syntax for the .prop modifier
      if (process.env.VBIND_PROP_SHORTHAND && propBindRE.test(name)) {
        (modifiers || (modifiers = {})).prop = true
        name = `.` + name.slice(1).replace(modifierRE, '')
      } else if (modifiers) {
        name = name.replace(modifierRE, '')
      }
      if (bindRE.test(name)) {
        // v-bind
        name = name.replace(bindRE, '')
        value = parseFilters(value)
        isDynamic = dynamicArgRE.test(name)
        if (isDynamic) {
          name = name.slice(1, -1)
        }
        if (
          process.env.NODE_ENV !== 'production' &&
          value.trim().length === 0
        ) {
          warn(
            `The value for a v-bind expression cannot be empty. Found in "v-bind:${name}"`
          )
        }
        if (modifiers) {
          if (modifiers.prop && !isDynamic) {
            name = camelize(name)
            if (name === 'innerHtml') name = 'innerHTML'
          }
          if (modifiers.camel && !isDynamic) {
            name = camelize(name)
          }
          if (modifiers.sync) {
            syncGen = genAssignmentCode(value, `$event`)
            if (!isDynamic) {
              addHandler(
                el,
                `update:${camelize(name)}`,
                syncGen,
                null,
                false,
                warn,
                list[i]
              )
              if (hyphenate(name) !== camelize(name)) {
                addHandler(
                  el,
                  `update:${hyphenate(name)}`,
                  syncGen,
                  null,
                  false,
                  warn,
                  list[i]
                )
              }
            } else {
              // handler w/ dynamic event name
              addHandler(
                el,
                `"update:"+(${name})`,
                syncGen,
                null,
                false,
                warn,
                list[i],
                true // dynamic
              )
            }
          }
        }
        if (
          (modifiers && modifiers.prop) ||
          (!el.component && platformMustUseProp(el.tag, el.attrsMap.type, name))
        ) {
          addProp(el, name, value, list[i], isDynamic)
        } else {
          addAttr(el, name, value, list[i], isDynamic)
        }
      } else if (onRE.test(name)) {
        // v-on
        name = name.replace(onRE, '')
        isDynamic = dynamicArgRE.test(name)
        if (isDynamic) {
          name = name.slice(1, -1)
        }
        addHandler(el, name, value, modifiers, false, warn, list[i], isDynamic)
      } else {
        // normal directives
        name = name.replace(dirRE, '')
        // parse arg
        const argMatch = name.match(argRE)
        let arg = argMatch && argMatch[1]
        isDynamic = false
        if (arg) {
          name = name.slice(0, -(arg.length + 1))
          if (dynamicArgRE.test(arg)) {
            arg = arg.slice(1, -1)
            isDynamic = true
          }
        }
        addDirective(
          el,
          name,
          rawName,
          value,
          arg,
          isDynamic,
          modifiers,
          list[i]
        )
        if (process.env.NODE_ENV !== 'production' && name === 'model') {
          checkForAliasModel(el, value)
        }
      }
    } else {
      // literal attribute
      if (process.env.NODE_ENV !== 'production') {
        const res = parseText(value, delimiters)
        if (res) {
          warn(
            `${name}="${value}": ` +
              'Interpolation inside attributes has been removed. ' +
              'Use v-bind or the colon shorthand instead. For example, ' +
              'instead of <div id="{{ val }}">, use <div :id="val">.',
            list[i]
          )
        }
      }
      addAttr(el, name, JSON.stringify(value), list[i])
      // #6887 firefox doesn't update muted state if set via attribute
      // even immediately after element creation
      if (
        !el.component &&
        name === 'muted' &&
        platformMustUseProp(el.tag, el.attrsMap.type, name)
      ) {
        addProp(el, name, 'true', list[i])
      }
    }
  }
}

export function addHandler(
  el: ASTElement,
  name: string,
  value: string,
  modifiers?: ASTModifiers | null,
  important?: boolean,
  warn?: Function,
  range?: Range,
  dynamic?: boolean
) {
  modifiers = modifiers || emptyObject
  // warn prevent and passive modifier
  /* istanbul ignore if */
  if (
    process.env.NODE_ENV !== 'production' &&
    warn &&
    modifiers.prevent &&
    modifiers.passive
  ) {
    warn(
      "passive and prevent can't be used together. " +
        "Passive handler can't prevent default event.",
      range
    )
  }

  // normalize click.right and click.middle since they don't actually fire
  // this is technically browser-specific, but at least for now browsers are
  // the only target envs that have right/middle clicks.
  if (modifiers.right) {
    if (dynamic) {
      name = `(${name})==='click'?'contextmenu':(${name})`
    } else if (name === 'click') {
      name = 'contextmenu'
      delete modifiers.right
    }
  } else if (modifiers.middle) {
    if (dynamic) {
      name = `(${name})==='click'?'mouseup':(${name})`
    } else if (name === 'click') {
      name = 'mouseup'
    }
  }

  // check capture modifier
  if (modifiers.capture) {
    delete modifiers.capture
    name = prependModifierMarker('!', name, dynamic)
  }
  if (modifiers.once) {
    delete modifiers.once
    name = prependModifierMarker('~', name, dynamic)
  }
  /* istanbul ignore if */
  if (modifiers.passive) {
    delete modifiers.passive
    name = prependModifierMarker('&', name, dynamic)
  }

  let events
  if (modifiers.native) {
    delete modifiers.native
    events = el.nativeEvents || (el.nativeEvents = {})
  } else {
    events = el.events || (el.events = {})
  }

  const newHandler: any = rangeSetItem({ value: value.trim(), dynamic }, range)
  if (modifiers !== emptyObject) {
    newHandler.modifiers = modifiers
  }

  const handlers = events[name]
  /* istanbul ignore if */
  if (Array.isArray(handlers)) {
    important ? handlers.unshift(newHandler) : handlers.push(newHandler)
  } else if (handlers) {
    events[name] = important ? [newHandler, handlers] : [handlers, newHandler]
  } else {
    events[name] = newHandler
  }

  el.plain = false
}

生成渲染代码时通过genHandlers将事件绑定至data部分

export function genHandlers(
  events: ASTElementHandlers,
  isNative: boolean
): string {
  const prefix = isNative ? 'nativeOn:' : 'on:'
  let staticHandlers = ``
  let dynamicHandlers = ``
  for (const name in events) {
    const handlerCode = genHandler(events[name])
    //@ts-expect-error
    if (events[name] && events[name].dynamic) {
      dynamicHandlers += `${name},${handlerCode},`
    } else {
      staticHandlers += `"${name}":${handlerCode},`
    }
  }
  staticHandlers = `{${staticHandlers.slice(0, -1)}}`
  if (dynamicHandlers) {
    return prefix + `_d(${staticHandlers},[${dynamicHandlers.slice(0, -1)}])`
  } else {
    return prefix + staticHandlers
  }
}

渲染到页面时调用路径为_update->__patch__->createElm->invokeCreateHooks->updateListeners->updateListeners->add最终将事件绑定到DOM元素上。

指令

v-show和v-model为两个内置指令

import("../vue.study.esm.js").then((module) => {
  const { Vue } = module;

  const app = new Vue({
    data() {
      return {
        value: 1,
      };
    },
    template: "<span v-on:click='value++'>{{value}}<span v-show='value%2' style='display: block;'>Test</span></span>"
  });
  app.$mount("#app");
});

在解析AST时处理标签结尾时调用closeElement->processElement->processAttrs->addDirective在节点增加属性directives，在渲染函数函数中也是陪配置到第二个参数的directives数组，生成到vNode的data.directives。渲染到页面时调用路径为_update->__patch__->createElm->invokeCreateHooks->updateDirectives->_update从vm.$options解析出指令定义，并依据情况调用具体钩子。其中v-show和v-model分别定义在src\platforms\web\runtime\directives\show.ts和src\platforms\web\runtime\directives\model.ts

v-show主要设置el.style.display，v-model， 补充实验组件上的v-model

import("../vue.study.esm.js").then((module) => {
  const { Vue } = module;

  const app = new Vue({
    data() {
      return {
        value: '',
        value2: ''
      };
    },
    template: 
      `<div>
        <input v-model="value" />
        {{value}}
        <select v-model="value2">
          <option value="">--Please choose an option--</option>
          <option value="dog">Dog</option>
          <option value="cat">Cat</option>
          <option value="hamster">Hamster</option>
          <option value="parrot">Parrot</option>
          <option value="spider">Spider</option>
          <option value="goldfish">Goldfish</option>
        </select>
        {{value2}}
      </div>`
  });
  app.$mount("#app");
});