判断是否存在某个字段hasOwnProperty

<script type="text/javascript">

        var obj = {

            a: 1,

            fn: function(){

 

            },

            c:{

                d: 5

            }

        };

        console.log(obj.hasOwnProperty('a'));//true

        console.log(obj.hasOwnProperty('fn'));//true

        console.log(obj.hasOwnProperty('c'));//true

        console.log(obj.c.hasOwnProperty('d'));//true

        console.log(obj.hasOwnProperty('d'));//false, obj对象没有d属性

        var str = new String();

        console.log(str.hasOwnProperty('substring'));//false

        console.log(String.prototype.hasOwnProperty('substring'));//true

    </script>