js拷贝实例；

var arr1 = ["x","y",[,]];
        // var arr2 =arr1.slice(0);
        //     arr1[0] ="z";
        //     arr1[2][0] = "v";
        //     console.log(arr1[2][0]); //浅拷贝
        var str = JSON.stringify(arr1);//"["x","y",[1,2]]";
        var str1 = JSON.parse(str);
        arr1[][] = "s";
        console.log(arr1[][]);
        console.log(str1[][]);
        console.log(str1);
        console.log(arr1);         //深拷贝