vue.js 源代码学习笔记 ----- text-parse.js

/* @flow */

import { cached } from 'shared/util'
import { parseFilters } from './filter-parser'

//找到{{abc}}这样的
const defaultTagRE = /\{\{((?:.|\n)+?)\}\}/g   //.+的意义是最小匹配, 找到符合的马上结束

//正则的元字符  ^ $ . * + ? = ! : | \ / ( ) [ ] { }
const regexEscapeRE = /[-.*+?^${}()|[\]/\\]/g

//这个函数创建用户自定义模板符号, 比如传入 [  "[[", "]]" ], 模板就可以写成 [[abc.reverse()]]
const buildRegex = cached(delimiters => {
  const open = delimiters[0].replace(regexEscapeRE, '\\$&')   //$&代表这个匹配项, 这里元字符使用\\转义, 保证安全
  const close = delimiters[1].replace(regexEscapeRE, '\\$&')
  return new RegExp(open + '((?:.|\\n)+?)' + close, 'g')      //格式跟 defaultTagRe类似
})

export function parseText (
  text: string,
  delimiters?: [string, string]
): string | void {
　//拿到最终的模板正则　
  const tagRE = delimiters ? buildRegex(delimiters) : defaultTagRE
  if (!tagRE.test(text)) {
    return
  }
  const tokens = []
  let lastIndex = tagRE.lastIndex = 0
  let match, index
  while ((match = tagRE.exec(text))) {
    index = match.index
    // push text token
    if (index > lastIndex) {
      tokens.push(JSON.stringify(text.slice(lastIndex, index)))
    }
    // tag token
    const exp = parseFilters(match[1].trim())
    tokens.push(`_s(${exp})`)
    lastIndex = index + match[0].length
  }
  if (lastIndex < text.length) {
    tokens.push(JSON.stringify(text.slice(lastIndex)))
  }
  return tokens.join('+')
}