JavaScript 使用中括号索引查找字符串中的第N个到最后一个字符
// 举例
var firstName = "Ada";
var thirdToLastLetterOfFirstName = firstName[firstName.length - 3];
// Setup
var lastName = "Lovelace";
// Only change code below this line
var secondToLastLetterOfLastName = lastName[lastName.length - 2];