数组-2

    join(separator)
    var arr = ["旋之华", 18, "男"];
    var str = arr.join("|");
    console.log(str);
    console.log(typeof str); // string
    console.log(arr);
    将数组的元素组成一个字符串，以separator为分隔符，默认为,

    // push()和pop()  数组的最后操作
    var arr = ["张三", "李四", "王五"];
    var count = arr.push("赵六", "宋小宝");
    console.log(count);
    console.log(arr);

    var item = arr.pop();
    console.log(item);
    console.log(arr);

 var arr = ["张三", "李四", "王五"];
 console.log(arr.reverse());
 console.log(arr);

 concat()
 var arr = [1, 3, 5, 7, 9];
 var copyArr =  arr.concat(11, "王小二", ["张三", "李四"]);

 // shift() 和 unshift()  shift()是删除第一项，返回被删除元素的值，如果数组为空返回Undefined   unshift返回数组的长度
 var arr = ["张三", "李四", "王五"];
 console.log(arr.shift());
 console.log(arr.shift());
 var count = arr.unshift("小沈阳", "宋小宝");

// indexOf()和 lastIndexOf()
 var arr = [2, 4, 6, 8, 8, 6, 4, 2];
 console.log(arr.indexOf(4, 2));//-1
 console.log(arr.indexOf(4));  //1
 console.log(arr.lastIndexOf(4));  //6 从后往前找
 console.log(arr.indexOf("4")); // -1
 console.log(arr.lastIndexOf("4")); // -1