1. splice 增，删，改
    2.  /*shift   pop*/
    3.         var arr = [4,5,6,7,8]
    4.         /*
    5.         splice(index,howmany)
    6.         index--从那个下标开始删除
    7.         howmany删除几个
    8.         */
    9.         arr.splice(2,2)
    10.         console.log(arr)
    1.  /*
    2.         修改  "vue"
    4.         splice(index,howmany,value)
    5.         index 下标
    6.         howmany  删除多少个
    7.         value 替代的值
    8.         */
    9.        var arr = ["html","css","javascript"];
    10.        arr.splice(1,1,"vue")
    11.        console.log(arr)
    1.  /*splice 增加
    2.         从下标的前面添加
    3.         splice(index,0,value...)
    4.         */
    5.         var arr = [3,4,5,6]
    6.         arr.splice(2,0,"html","css");
    7.         console.log(arr)
    1.  /*增，删，改，*/
    2.         var arr = [3,4,5,6];
    3.         /*
    4.         [3,4,"html",5,6]
    5.         splice(index,0,value)
    6.         */
    7.        arr.splice(2,0,"html");
    8.        console.log(arr)
    10.        /* 
    11.        删除
    12.        splice(index,howmany)
    13.        */
    14.       var test = [1,2,3,4,5]
    15.       //[1,4,5]
    16.       test.splice(1,2);
    17.       console.log(test)
    1.  var arr = [2,3,4,5]
    2.         //[2,3,"vue",5]
    3.         //arr.splice(index,howmany...value)
    4.         arr.splice(2,1,"vue")
    5.         console.log(arr)