js：常见对象的类型判断typeof和布尔值Boolean

typeof function(){} 'function'
typeof {} 'object'
typeof [] 'object'
typeof '' 'string'
typeof 0 'number'
typeof true 'boolean'
typeof null 'object'
typeof undefined 'undefined'
typeof [].length 'number'
typeof {}.length 'undefined'

Boolean(function(){}) true
Boolean({}) true
Boolean([]) true
Boolean(null) false
Boolean(undefined) false
Boolean('') false
Boolean(' ') true
Boolean(0) false
Boolean(1) true
Boolean(false) false
Boolean(true) true