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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
</body>
<script>
// 构造JavaScript ast
const State = {
initial: 1, // 初始状态
tagOpen: 2, // 标签开始状态
tagName: 3, // 标签名称状态
text: 4, // 文本状态
tagEnd: 5, // 结束标签状态
tagEndName: 6 // 结束标签名称状态
}
const isAlpha = (char) => { // 用于判断是否是字母
return char >= 'a' && char <= 'z' || char >= 'A' && char <= 'Z'
}
const tokenize = (str) => { // 用于切割模板，返回token数组
let currentState = State.initial
const chars = [] // 用于缓存字符
const tokens = [] // 存储生成的token，并作为函数返回值进行返回
while (str) { // 使用while循环开启自动机，只要str没有被消费尽，自动机就会一直运行
const char = str[0]
switch (currentState) {
case State.initial:
if (char === '<') {
currentState = State.tagOpen
str = str.slice(1)
} else if (isAlpha(char)) {
currentState = State.text
chars.push(char)
str = str.slice(1)
}
break;
case State.tagOpen:
if (isAlpha(char)) {
currentState = State.tagName
chars.push(char)
str = str.slice(1)
} else if (char === '/') {
currentState = State.tagEnd
str = str.slice(1)
}
break;
case State.tagName:
if (isAlpha(char)) {
chars.push(char)
str = str.slice(1)
} else if (char === '>') {
currentState = State.initial
tokens.push({
type: 'tag',
name: chars.join('')
})
chars.length = 0
str = str.slice(1)
}
break;
case State.text:
if (isAlpha(char)) {
chars.push(char)
str = str.slice(1)
} else if (char === '<') {
currentState = State.tagOpen
tokens.push({
type: 'text',
content: chars.join('')
})
chars.length = 0
str = str.slice(1)
}
break;
case State.tagEnd:
if (isAlpha(char)) {
currentState = State.tagEndName
chars.push(char)
str = str.slice(1)
}
break;
case State.tagEndName:
if (isAlpha(char)) {
chars.push(char)
str = str.slice(1)
} else if (char === '>') {
currentState = State.initial
tokens.push({
type: 'tagEnd',
name: chars.join('')
})
chars.length = 0
str = str.slice(1)
}
break;
}
}
return tokens
}
const parse = (str) => { // 解析器，返回模板ast
const tokens = tokenize(str)
const root = {
type: 'Root',
children: []
}
const elementStack = [root] // 及其重要，构造父子关系的关键角色
while (tokens.length) {
const parent = elementStack.at(-1)
const t = tokens[0]
switch (t.type) {
case 'tag':
const elementNode = {
type: 'Element',
tag: t.name,
children: []
}
parent.children.push(elementNode)
elementStack.push(elementNode)
break;
case 'text':
const textNode = {
type: 'Text',
content: t.content
}
parent.children.push(textNode)
break;
case 'tagEnd':
elementStack.pop()
break;
}
tokens.shift()
}
return root
}
const dump = (node, indent = 0) => {
const type = node.type
const desc = node.type === 'Root' ? '' : node.type === 'Element' ? node.tag : node.content
console.log(`${'-'.repeat(indent)}${type}:${desc}`);
if (node.children) {
node.children.forEach(n => dump(n, indent + 2))
}
}
const traverseNode = (ast, context) => { // 遍历节点
context.currentNode = ast
const exitFns = [] // 退出阶段的回调函数数组
const transforms = context.nodeTransforms
for (let i = 0; i < transforms.length; i++) {
const onExit = transforms[i](context.currentNode, context)
if (onExit) { // 通过转换函数返回一个函数，将该函数作为退出阶段的回调函数添加到exitFns数组中
exitFns.push(onExit)
}
if (!context.currentNode) return // 当前节点被移除后，停止执行后续转换函数
}
const children = context.currentNode.children
if (children) {
for (let i = 0; i < children.length; i++) {
context.parent = context.currentNode
context.childIndex = i
traverseNode(children[i], context)
}
}
// 在节点处理的最后阶段执行缓存到exitFns中的回调函数(回到上一个traverseNode函数中)
// 注意这里需要从末尾函数开始往前执行
let i = exitFns.length
while (i--) {
exitFns[i]()
}
}
const transformElement = (node) => { // 转换函数
// if (node.type === 'Element' && node.tag === 'p') {
// node.tag = 'h1'
// }
return () => {
// 返回一个在退出阶段执行的回调函数，当这里代码执行时当前转换节点的子节点一定都处理完毕了
if (node.type !== 'Element') return;
const callExp = createCallExpression('h', [
createStringLiteral(node.tag)
])
node.children.length === 1 ? callExp.arguments.push(node.children[0].jsNode) : callExp.arguments.push(createArrayExpression(node.children.map(c => c.jsNode)))
node.jsNode = callExp
}
}
const transformText = (node, context) => { // 转换函数
// if (node.type === 'Text') {
// // node.content = node.content.repeat(2)
// context.replaceNode({
// type: 'Element',
// tag: 'span'
// })
// }
if (node.type !== 'Text') return;
node.jsNode = createStringLiteral(node.content)
}
const transformRoot = (node) => {
return () => {
if (node.type !== 'Root') return;
const vnodeJSast = node.children[0].jsNode
node.jsNode = {
type: 'FunctionDecl',
id: {type: 'Identifier', name: 'render'},
params: [],
body: [
{
type: 'ReturnStatement',
return: vnodeJSast
}
]
}
}
}
// const removeText = (node, context) => { // 转换函数
// if (node.type === 'Text') {
// context.removeNode()
// }
// }
const transform = (ast) => { // 转换函数，返回JavaScript ast
const context = { // 上下文数据
currentNode: null,
childIndex: 0,
parent: null,
nodeTransforms: [
transformElement,
transformText,
transformRoot
// removeText
],
replaceNode (node) { // 替换ast中的节点
context.parent.children[context.childIndex] = node
context.currentNode = node
},
removeNode () { // 移除ast中的节点
context.parent.children.splice(context.childIndex, 1)
context.currentNode = null
}
}
traverseNode(ast, context)
dump(ast)
}
const createStringLiteral = (value) => { // 用来创建StringLiteral节点
return {
type: 'StringLiteral',
value
}
}
const createIdentifier = (name) => { // 用来创建Identifier节点
return {
type: 'Identifier',
name
}
}
const createArrayExpression = (elements) => { // 用来创建ArrayExpression节点
return {
type: 'ArrayExpression',
elements
}
}
const createCallExpression = (callee, arguments) => { // 用来创建CallExpression节点
return {
type: 'CallExpression',
callee: createIdentifier(callee),
arguments
}
}
const genNodeList = (nodes, context) => {
const {push} = context
for (let i = 0; i < nodes.length; i++) {
const node = nodes[i]
genNode(node, context)
if (i < nodes.length - 1) {
push(', ')
}
}
}
const genFunctionDecl = (node, context) => {
const {push, indent, deIndent} = context
push(`function ${node.id.name}`)
push('(')
genNodeList(node.params, context)
push(') ')
push('{')
indent()
node.body.forEach(n => genNode(n, context))
deIndent(),
push('}')
}
const genReturnStatement = (node, context) => {
const {push} = context
push('return ')
genNode(node.return, context)
}
const genStringLiteral = (node, context) => {
const {push} = context
push(`${node.value}`)
}
const genCallExpression = (node, context) => {
const {push} = context
const {callee, arguments: args} = node
push(`${callee.name}(`)
genNodeList(args, context)
push(')')
}
const genArrayExpression = (node, context) => {
const {push} = context
push('[')
genNodeList(node.elements, context)
push(']')
}
// console.log(ast.jsNode); // 模板ast所对应的JavaScript ast就存储在ast根节点的jsNode中
const genNode = (node, context) => { // 匹配不同类型节点，并调用与之对应的生成器函数
switch (node.type) {
case 'FunctionDecl':
genFunctionDecl(node, context)
break;
case 'ReturnStatement':
genReturnStatement(node, context)
break;
case 'CallExpression':
genCallExpression(node, context)
break;
case 'StringLiteral':
genStringLiteral(node, context)
break;
case 'ArrayExpression':
genArrayExpression(node, context)
break;
}
}
const generate = (node) => { // node: JavaScript ast
console.log(node);
const context = { // 上下文
code: '', // 存储最终生成的渲染函数代码
push(code) {
context.code += code
},
currentIndent: 0,
newline() { // 换行函数
context.code += '\n' + ` `.repeat(context.currentIndent)
},
indent() { // 用来进行缩进
context.currentIndent++
context.newline()
},
deIndent() { // 用来取消缩进
context.currentIndent--
context.newline()
}
}
genNode(node, context) // 代码生成本质上是字符串拼接的艺术
return context.code
}
const compile = (template) => { // 编译函数
const ast = parse(template) // 获取模板ast
transform(ast)
const code = generate(ast.jsNode)
return code
}
const code = compile('<div><p>vue</p><p>template</p></div>')
console.log(code, 'code');
</script>
</html>