vue模板编译原理-轻识

我们都知道 vue 写代码是需要按照固定的格式，比如下面这样：

<template>  <div>{{msg}}</div></template>
<script>export default {  data () {    return {      msg: ''    }  }}</script>

把 html 的内容写在 template 里面，经过 vue 的处理，首先会把模板转换为 AST 抽象语法树，然后把 AST 转换为可执行的 render 函数，最后才可以生成真是 DOM，那么今天要分析的内容是如何将模板生成 AST 的。

首先要生成的 AST 结构如下：

function createASTElement (  tag,  attrs,  parent) {  return {    type: 1,    tag: tag,    attrsList: attrs,    attrsMap: attrs,    rawAttrsMap: {},    parent: parent,    children: []  }}

然后就是把模板的内容都遍历一遍，通过正则去匹配标签的内容。

var unicodeRegExp = /a-zA-Z\u00B7\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u037D\u037F-\u1FFF\u200C-\u200D\u203F-\u2040\u2070-\u218F\u2C00-\u2FEF\u3001-\uD7FF\uF900-\uFDCF\uFDF0-\uFFFD/;// Regular Expressions for parsing tags and attributesvar attribute = /^\s*([^\s"'<>\/=]+)(?:\s*(=)\s*(?:"([^"]*)"+|'([^']*)'+|([^\s"'=<>`]+)))?/;var dynamicArgAttribute = /^\s*((?:v-[\w-]+:|@|:|#)\[[^=]+?\][^\s"'<>\/=]*)(?:\s*(=)\s*(?:"([^"]*)"+|'([^']*)'+|([^\s"'=<>`]+)))?/;var ncname = "[a-zA-Z_][\\-\\.0-9_a-zA-Z" + (unicodeRegExp.source) + "]*";var qnameCapture = "((?:" + ncname + "\\:)?" + ncname + ")";var startTagOpen = new RegExp(("^<" + qnameCapture));var startTagClose = /^\s*(\/?)>/;var endTag = new RegExp(("^<\\/" + qnameCapture + "[^>]*>"));var doctype = /^<!DOCTYPE [^>]+>/i;// #7298: escape - to avoid being passed as HTML comment when inlined in pagevar reCache = {};var comment = /^<!\--/;var conditionalComment = /^<!\[/;

这些正则都是源码里面粘贴过来的，包括匹配开始标签，结束标签，注释等等。

function parseHTML(html, options) {  var stack = [];  var expectHTML = options.expectHTML;  var isUnaryTag$$1 = options.isUnaryTag || no;  var canBeLeftOpenTag$$1 = options.canBeLeftOpenTag || no;  var index = 0;  var last, lastTag;  while (html) {    last = html;    // 确保不是 script 或者 style 者 textarea 标签    if (!lastTag || !isPlainTextElement(lastTag)) {      var textEnd = html.indexOf('<');      if (textEnd === 0) {        // End tag: 匹配结束标签        var endTagMatch = html.match(endTag);        if (endTagMatch) {          var curIndex = index;          advance(endTagMatch[0].length);          parseEndTag(endTagMatch[1], curIndex, index);          continue        }
        // Start tag: 匹配开始标签        var startTagMatch = parseStartTag();        if (startTagMatch) {          handleStartTag(startTagMatch);          continue        }      }
      var text = (void 0), rest = (void 0), next = (void 0);      if (textEnd >= 0) {        rest = html.slice(textEnd);        while (          !endTag.test(rest) &&          !startTagOpen.test(rest)        ) {          // 把标签里面的文字提取出来 hello</div> 提取 hello          next = rest.indexOf('<', 1);          if (next < 0) { break }          textEnd += next;          rest = html.slice(textEnd);        }        text = html.substring(0, textEnd);      }
      if (textEnd < 0) {        text = html;      }      if (text) {        advance(text.length); // 去除文字 hello 剩下 </div>      }
      if (options.chars && text) {        options.chars(text, index - text.length, index);      }    } else {      var endTagLength = 0;      var stackedTag = lastTag.toLowerCase();      var reStackedTag = reCache[stackedTag] || (reCache[stackedTag] = new RegExp('([\\s\\S]*?)(</' + stackedTag + '[^>]*>)', 'i'));      var rest$1 = html.replace(reStackedTag, function (all, text, endTag) {        endTagLength = endTag.length;        return ''      });      index += html.length - rest$1.length;      html = rest$1;      parseEndTag(stackedTag, index - endTagLength, index);    }  }
  // Clean up any remaining tags  parseEndTag();
  function advance(n) {    index += n;    html = html.substring(n);  }
  function parseStartTag() {    var start = html.match(startTagOpen);    // [ '<div', 'div', index: 0, input: '<div id="1" bg="2">hello</div>', groups: undefined ]    if (start) {      var match = {        tagName: start[1],        attrs: [],        start: index      };      advance(start[0].length); // 去除 <div，剩下 id="1" bg="2">hello</div>      var end, attr;      // 把属性都存储起来 id="1" bg="2" 去除属性之后剩下 >hello</div>      while (!(end = html.match(startTagClose)) && (attr = html.match(dynamicArgAttribute) || html.match(attribute))) {        attr.start = index;        advance(attr[0].length);        attr.end = index;        match.attrs.push(attr);      }      if (end) {        match.unarySlash = end[1];        advance(end[0].length); // 把>或者/>去除剩下 hello</div>        match.end = index;        return match      }    }  }
  function handleStartTag(match) {    var tagName = match.tagName;    var unarySlash = match.unarySlash; // 自闭合标签为/ 双标签为‘’空
    var unary = !!unarySlash;
    var l = match.attrs.length;    var attrs = new Array(l);    for (var i = 0; i < l; i++) {      var args = match.attrs[i];      var value = args[3] || args[4] || args[5] || '';      attrs[i] = {        name: args[1],        value: value      };      // 按照{ name: value } 的形式保存起来，{ id: 1 }      if (options.outputSourceRange) {        attrs[i].start = args.start + args[0].match(/^\s*/).length;        attrs[i].end = args.end;      }    }    // 双标签    if (!unary) {      stack.push({ tag: tagName, lowerCasedTag: tagName.toLowerCase(), attrs: attrs, start: match.start, end: match.end });      lastTag = tagName;    }    if (options.start) {      options.start(tagName, attrs, unary, match.start, match.end);    }  }  // stackedTag, index - endTagLength, index  function parseEndTag(tagName, start, end) {    var pos, lowerCasedTagName;    if (start == null) { start = index; }    if (end == null) { end = index; }
    // Find the closest opened tag of the same type    if (tagName) {      lowerCasedTagName = tagName.toLowerCase();      for (pos = stack.length - 1; pos >= 0; pos--) {        if (stack[pos].lowerCasedTag === lowerCasedTagName) {          break        }      }    } else {      // If no tag name is provided, clean shop      pos = 0;    }    if (pos >= 0) {      // Close all the open elements, up the stack      for (var i = stack.length - 1; i >= pos; i--) {        if (options.end) {          options.end(stack[i].tag, start, end);        }      }      // Remove the open elements from the stack      stack.length = pos;      lastTag = pos && stack[pos - 1].tag;    }  }}

上面是把所有的标签进行处理，按照顺序遍历之后就可以生成 AST 了。

var currentParent;var stack = [];var root;
function end(tag, start) {  var element = stack[stack.length - 1];  // pop stack 出栈  stack.length -= 1;  currentParent = stack[stack.length - 1];  closeElement(element);}
function start(tag, attrs, unary, start, end) {  var element = createASTElement(tag, attrs, currentParent);  if (!root) {    root = element;  }  if (!unary) {    currentParent = element;    // push stack 入栈    stack.push(element);  }}
function chars(text, start, end) {  var children = currentParent.children;  if (text) {    var child;    child = {      type: 2,      expression: '',      tokens: '',      text: text    };    if (child) {      children.push(child);    }  }}
function closeElement (element) {  if (currentParent && !element.forbidden) {    currentParent.children.push(element);    element.parent = currentParent;  }  element.children = element.children.filter(function (c) { return !(c).slotScope; });}
function createASTElement (  tag,  attrs,  parent) {  return {    type: 1,    tag: tag,    attrsList: attrs,    attrsMap: attrs,    rawAttrsMap: {},    parent: parent,    children: []  }}
const content = '<template><div bg="1">hello<span>11</span></div></template>'
parseHTML(content, {  start: start,  end: end,  chars: chars});
console.log(root) // ast

源码在 vue-template-compiler