详解Vue源码中一些util函数

const _toString = Object.prototype.toString
var obj = {}

obj.toString() // [object Object]
_toString.call(obj) // [object Object]

obj.toString = () => '111'

obj.toString() // 111
_toString.call(obj) // [object Object]

/hello/.toString() // /hello/
_toString.call(/hello/) // [object RegExp]

function toRawType (value) {
 return _toString.call(value).slice(8, -1)
}

toRawType(null) // "Null"
toRawType(/sdfsd/) //"RegExp"

function computed(str) {
 // 假设中间的计算非常耗时
 console.log('2000s have passed')
 return 'a result'
}

function cached(fn){
 const cache = Object.create(null)
 return function cachedFn (str) {
  if ( !cache[str] ) {
    cache[str] = fn(str)
  }
  return cache[str]
 }
}

var cachedComputed = cached(computed)
cachedComputed('ss')
// 打印2000s have passed
cachedComputed('ss')
// 不再打印

const camelizeRE = /-(\w)/g
const camelize = cached((str) => {
 return str.replace(camelizeRE, (_, c) => c ? c.toUpperCase() : '')
})

camelize('hello-world')
// "helloWorld"

const inBrowser = typeof window !== 'undefined'

const inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform
const weexPlatform = inWeex && WXEnvironment.platform.toLowerCase()

const UA = inBrowser && window.navigator.userAgent.toLowerCase()

const isIE = UA && /msie|trident/.test(UA)
const isIE9 = UA && UA.indexOf('msie 9.0') > 0
const isEdge = UA && UA.indexOf('edge/') > 0
const isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android')
const isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios')
const isChrome = UA && /chrome\/\d+/.test(UA) && !isEdge
const isPhantomJS = UA && /phantomjs/.test(UA)
const isFF = UA && UA.match(/firefox\/(\d+)/)

console.log.toString()
// "function log() { [native code] }"

function fn(){}
fn.toString()
// "function fn(){}"

// 所以
function isNative (Ctor){
 return typeof Ctor === 'function' && /native code/.test(Ctor.toString())
}