js判断是否为对象

• toString

Object.prototype.toString.call(obj) === '[object Object]'   => true
Object.prototype.toString.call(arr) === '[object Array]'    => true

• constructor

obj.constructor === Object   => true
arr.constructor === Array    => true

• instanceof

obj instaceof Object   => true
arr instaceof Object   => true
obj instaceof Array    => false
arr instaceof Array    => true

• typeof

表达式                       返回值
typeof undefined           'undefined'
typeof null                'object'
typeof true                'boolean'
typeof 123                 'number'
typeof "abc"               'string'
typeof function() {}       'function'
typeof {}                  'object'
typeof []                  'object'

• jquery方法

$.isPlainObject(obj) 
$.isArray(arr)
$.isFunction(fn)