WEEX H5 Render 解读（6）之console类

weex对console类进行了一个封装，我们在程序里调用的console.log()不再直接是直接调用系统的了，而是调用Weex的封装了。下面我们就读读weex如何封装的console。

---

console.js所在的位置是：

const { console, nativeLog } = global
const LEVELS = ['error', 'warn', 'info', 'log', 'debug']
const levelMap = {}

generateLevelMap()

/* istanbul ignore if */
if (
  typeof console === 'undefined' || // Android
  (global.WXEnvironment && global.WXEnvironment.platform === 'iOS') // iOS
) {
  global.console = {
    debug: (...args) => {
      if (checkLevel('debug')) { nativeLog(...format(args), '__DEBUG') }
    },
    log: (...args) => {
      if (checkLevel('log')) { nativeLog(...format(args), '__LOG') }
    },
    info: (...args) => {
      if (checkLevel('info')) { nativeLog(...format(args), '__INFO') }
    },
    warn: (...args) => {
      if (checkLevel('warn')) { nativeLog(...format(args), '__WARN') }
    },
    error: (...args) => {
      if (checkLevel('error')) { nativeLog(...format(args), '__ERROR') }
    }
  }
}
else { // HTML5
  const { debug, log, info, warn, error } = console
  console.__ori__ = { debug, log, info, warn, error }
  console.debug = (...args) => {
    if (checkLevel('debug')) { console.__ori__.debug.apply(console, args) }
  }
  console.log = (...args) => {
    if (checkLevel('log')) { console.__ori__.log.apply(console, args) }
  }
  console.info = (...args) => {
    if (checkLevel('info')) { console.__ori__.info.apply(console, args) }
  }
  console.warn = (...args) => {
    if (checkLevel('warn')) { console.__ori__.warn.apply(console, args) }
  }
  console.error = (...args) => {
    if (checkLevel('error')) { console.__ori__.error.apply(console, args) }
  }
}

function generateLevelMap () {
  LEVELS.forEach(level => {
    const levelIndex = LEVELS.indexOf(level)
    levelMap[level] = {}
    LEVELS.forEach(type => {
      const typeIndex = LEVELS.indexOf(type)
      if (typeIndex <= levelIndex) {
        levelMap[level][type] = true
      }
    })
  })
}

function normalize (v) {
  const type = Object.prototype.toString.call(v)
  if (type.toLowerCase() === '[object object]') {
    v = JSON.stringify(v)
  }
  else {
    v = String(v)
  }
  return v
}

function checkLevel (type) {
  const logLevel = (global.WXEnvironment && global.WXEnvironment.logLevel) || 'log'
  return levelMap[logLevel] && levelMap[logLevel][type]
}

function format (args) {
  return args.map(v => normalize(v))
}



/** WEBPACK FOOTER **
 ** ./html5/shared/console.js
 **/

generateLevelMap ()是对日志事件做等级区分，即建立一个二维数组，比较任意两个的优先级。
normalize()是对参数v做json序列化工作。
if(){}else{}则是对console中的每个函数进行调用。比如当调用console.warn()是先检查这个日志等级是否高于当前的等级，然后调用相应方法。