let maxLength = 10; // 设maxLength为10
let arr = [0,1,2,3,4,5,6,7,8,9,10]; // 数组arr包含11项数据
let virtualData = arr.slice(0, maxLength); // virtualData截取了前10项数据[0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
let rest = arr[maxLength + 1]; // rest=arr[11]为undefined,
// rest为undefined,887行的countNumber++不会执行,导致后面的第n*countNumber+1不会加载, arr第11项数据10丢失了