如何实现这一目标
var has = Object.prototype.hasOwnProperty
var toString = Object.prototype.toString
function isEmpty(val) {
if (val == null) return true
if ('boolean' == typeof val) return false
if ('number' == typeof val) return val === 0
if ('string' == typeof val) return val.length === 0
if ('function' == typeof val) return val.length === 0
if (Array.isArray(val)) return val.length === 0
if (val instanceof Error) return val.message === ''
if (val.toString == toString) {
switch (val.toString()) {
case …
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