vue.js 源代码学习笔记 ----- codegen.js

/* @flow */

import { genHandlers } from './events'
import { baseWarn, pluckModuleFunction } from '../helpers'
import baseDirectives from '../directives/index'
import { camelize } from 'shared/util'

// configurable state
let warn
let transforms
let dataGenFns
let platformDirectives
let staticRenderFns
let onceCount
let currentOptions

export function generate (
  ast: ASTElement | void,
  options: CompilerOptions
): {
  render: string,
  staticRenderFns: Array<string>
} {
  // save previous staticRenderFns so generate calls can be nested
  const prevStaticRenderFns: Array<string> = staticRenderFns
  const currentStaticRenderFns: Array<string> = staticRenderFns = []
  const prevOnceCount = onceCount
  onceCount = 0
  currentOptions = options
  warn = options.warn || baseWarn
  transforms = pluckModuleFunction(options.modules, 'transformCode')
  dataGenFns = pluckModuleFunction(options.modules, 'genData')
  platformDirectives = options.directives || {}
  const code = ast ? genElement(ast) : '_h("div")'
  staticRenderFns = prevStaticRenderFns
  onceCount = prevOnceCount
  return {
    render: `with(this){return ${code}}`,
    staticRenderFns: currentStaticRenderFns
  }
}

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

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

// hoist static sub-trees out
function genStatic (el: ASTElement): string {
  el.staticProcessed = true
  staticRenderFns.push(`with(this){return ${genElement(el)}}`)
  return `_m(${staticRenderFns.length - 1}${el.staticInFor ? ',true' : ''})`
}

// v-once
function genOnce (el: ASTElement): string {
  el.onceProcessed = true
  if (el.if && !el.ifProcessed) {
    return genIf(el)
  } 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' && warn(
        `v-once can only be used inside v-for that is keyed. `
      )
      return genElement(el)
    }
    return `_o(${genElement(el)},${onceCount++}${key ? `,${key}` : ``})`
  } else {
    return genStatic(el)
  }
}

function genIf (el: any): string {
  el.ifProcessed = true // avoid recursion
  return genIfConditions(el.conditions)
}

function genIfConditions (conditions: ASTIfConditions): string {
  if (!conditions.length) {
    return '_e()'
  }

  var condition = conditions.shift()
  if (condition.exp) {
    return `(${condition.exp})?${genTernaryExp(condition.block)}:${genIfConditions(conditions)}`
  } else {
    return `${genTernaryExp(condition.block)}`
  }

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

function genFor (el: any): string {
  const exp = el.for
  const alias = el.alias
  const iterator1 = el.iterator1 ? `,${el.iterator1}` : ''
  const iterator2 = el.iterator2 ? `,${el.iterator2}` : ''
  el.forProcessed = true // avoid recursion
  return `_l((${exp}),` +
    `function(${alias}${iterator1}${iterator2}){` +
      `return ${genElement(el)}` +
    '})'
}

function genData (el: ASTElement): string {
  let data = '{'

  // directives first.
  // directives may mutate the el's other properties before they are generated.
  const dirs = genDirectives(el)
  if (dirs) data += dirs + ','

  // key
  if (el.key) {
    data += `key:${el.key},`
  }
  // ref
  if (el.ref) {
    data += `ref:${el.ref},`
  }
  if (el.refInFor) {
    data += `refInFor:true,`
  }
  // record original tag name for components using "is" attribute
  if (el.component) {
    data += `tag:"${el.tag}",`
  }
  // module data generation functions
  for (let i = 0; i < dataGenFns.length; i++) {
    data += dataGenFns[i](el)
  }
  // attributes
  if (el.attrs) {
    data += `attrs:{${genProps(el.attrs)}},`
  }
  // DOM props
  if (el.props) {
    data += `domProps:{${genProps(el.props)}},`
  }
  // event handlers
  if (el.events) {
    data += `${genHandlers(el.events)},`
  }
  if (el.nativeEvents) {
    data += `${genHandlers(el.nativeEvents, true)},`
  }
  // slot target
  if (el.slotTarget) {
    data += `slot:${el.slotTarget},`
  }
  // scoped slots
  if (el.scopedSlots) {
    data += `${genScopedSlots(el.scopedSlots)},`
  }
  // inline-template
  if (el.inlineTemplate) {
    const inlineTemplate = genInlineTemplate(el)
    if (inlineTemplate) {
      data += `${inlineTemplate},`
    }
  }
  data = data.replace(/,$/, '') + '}'
  // v-bind data wrap
  if (el.wrapData) {
    data = el.wrapData(data)
  }
  return data
}

function genDirectives (el: ASTElement): string | void {
  const dirs = el.directives
  if (!dirs) return
  let res = 'directives:['
  let hasRuntime = false
  let i, l, dir, needRuntime
  for (i = 0, l = dirs.length; i < l; i++) {
    dir = dirs[i]
    needRuntime = true
    const gen = platformDirectives[dir.name] || baseDirectives[dir.name]
    if (gen) {
      // compile-time directive that manipulates AST.
      // returns true if it also needs a runtime counterpart.
      needRuntime = !!gen(el, dir, 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:"${dir.arg}"` : ''
      }${
        dir.modifiers ? `,modifiers:${JSON.stringify(dir.modifiers)}` : ''
      }},`
    }
  }
  if (hasRuntime) {
    return res.slice(0, -1) + ']'
  }
}

function genInlineTemplate (el: ASTElement): ?string {
  const ast = el.children[0]
  if (process.env.NODE_ENV !== 'production' && (
    el.children.length > 1 || ast.type !== 1
  )) {
    warn('Inline-template components must have exactly one child element.')
  }
  if (ast.type === 1) {
    const inlineRenderFns = generate(ast, currentOptions)
    return `inlineTemplate:{render:function(){${
      inlineRenderFns.render
    }},staticRenderFns:[${
      inlineRenderFns.staticRenderFns.map(code => `function(){${code}}`).join(',')
    }]}`
  }
}

function genScopedSlots (slots) {
  return `scopedSlots:{${
    Object.keys(slots).map(key => genScopedSlot(key, slots[key])).join(',')
  }}`
}

function genScopedSlot (key: string, el: ASTElement) {
  return `${key}:function(${String(el.attrsMap.scope)}){` +
    `return ${el.tag === 'template'
      ? genChildren(el) || 'void 0'
      : genElement(el)
  }}`
}

function genChildren (el: ASTElement): string | void {
  if (el.children.length) {
    return '[' + el.children.map(genNode).join(',') + ']'
  }
}

function genNode (node: ASTNode) {
  if (node.type === 1) {
    return genElement(node)
  } else {
    return genText(node)
  }
}

function genText (text: ASTText | ASTExpression): string {
  return text.type === 2
    ? text.expression // no need for () because already wrapped in _s()
    : transformSpecialNewlines(JSON.stringify(text.text))
}

function genSlot (el: ASTElement): string {
  const slotName = el.slotName || '"default"'
  const children = genChildren(el)
  return `_t(${slotName}${
    children ? `,${children}` : ''
  }${
    el.attrs ? `${children ? '' : ',null'},{${
      el.attrs.map(a => `${camelize(a.name)}:${a.value}`).join(',')
    }}` : ''
  })`
}

// componentName is el.component, take it as argument to shun flow's pessimistic refinement
function genComponent (componentName, el): string {
  const children = el.inlineTemplate ? null : genChildren(el)
  return `_h(${componentName},${genData(el)}${
    children ? `,${children}` : ''
  })`
}

function genProps (props: Array<{ name: string, value: string }>): string {
  let res = ''
  for (let i = 0; i < props.length; i++) {
    const prop = props[i]
    res += `"${prop.name}":${transformSpecialNewlines(prop.value)},`
  }
  return res.slice(0, -1)
}

// #3895, #4268
function transformSpecialNewlines (text: string): string {
  return text
    .replace(/u2028/g, '\u2028')
    .replace(/u2029/g, '\u2029')
}