vue源码中的检测方法的实现

const isDef = (v) => {
 return v !== undefined && v !== null
}

const isPromise = (val) => {
 return (
  val !== undefine &&
  typeof val.then === 'function' &&
  typeof val.catch === 'function'
 )
}

const isPrimitive (value) => {
 return (
  typeof value === 'string' ||
  typeof value === 'number' ||
  typeof value === 'symbol' ||
  typeof value === 'boolean'
 )
}

const isPlainObject = (obj) => {
 return Object.prototype.toString.call(obj) === '[object Object]'
}

const isRegExp = (v) => {
 return Object.prototype.toString.call(v) === '[object RegExp]'
}

const hyphenateRE = /\B([A-Z])/g
const hyphenate = (str) => {
 return str.replace(hyphenateRE, '-$1').toLowerCase()
}

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

const cached = (fn) => {
  const cache = Object.create(null)
  console.log(cache);
  return ((str) => {
   const hit = cache[str]
   return hit || (cache[str] = fn(str))
  })
};

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