JS中string方法中常用方法之一：String.prototype.charAt()

String.prototype.charAt()返回字符串中指定位置的字符。
语法：str.charAt(index)（index 是0 到 字符串长度-1 的一个整数）
例子：输出字符串中不同位置的字符
//下例输出字符串 "Brave new world" 不同位置处的字符
var anyString = "Brave new world";

console.log("The character at index 0   is '" + anyString.charAt(0)   + "'");
console.log("The character at index 1   is '" + anyString.charAt(1)   + "'");
console.log("The character at index 2   is '" + anyString.charAt(2)   + "'");
console.log("The character at index 3   is '" + anyString.charAt(3)   + "'");
console.log("The character at index 4   is '" + anyString.charAt(4)   + "'");
console.log("The character at index 999 is '" + anyString.charAt(999) + "'");
//上面代码的输出为：
The character at index 0 is 'B'
The character at index 1 is 'r'
The character at index 2 is 'a'
The character at index 3 is 'v'
The character at index 4 is 'e'
The character at index 999 is ''