function reverseString(str)
 { // 第一步，使用split()方法，返回一個新數(shù)組 
// var splitString = "hello".split(""); 
var splitString = str.split(""); 
//將字符串拆分 // 返回一個新數(shù)組["h", "e", "l", "l", "o"] 
// 第二步，使用reverse()方法創(chuàng)建一個新數(shù)組 
// var reverseArray = ["h", "e", "l", "l", "o"].reverse(); 
var reverseArray = splitString.reverse(); 
// 原數(shù)組元素順序反轉(zhuǎn)["o", "l", "l", "e", "h"] 
// 第三步，使用join()方法將數(shù)組的每個元素連接在一起，組合成一個新字符串 
// var joinArray = ["o", "l", "l", "e", "h"].join(""); 
var joinArray = reverseArray.join(""); // "olleh" 
// 第四步，返回一個反轉(zhuǎn)的新字符串 return joinArray; 
// "olleh"}reverseString("hello"); 
// => olleh

function reverseString(str) {
 return str.split("").reverse().join("");
}reverseString("hello"); 
// => olleh

function reverseString(str) { 
// 第一步：創(chuàng)建一個空的字符串用來存儲新創(chuàng)建的字符串 var newString = ""; 
// 第二步：使用for循環(huán) 
// 循環(huán)從str.length-1開始做遞減遍歷,直到 i 大于或等于0，循環(huán)將繼續(xù)
 // str.length - 1對應的就是字符串最后一個字符o for (var i = str.length - 1; i >= 0; i--) {
 newString += str[i]; // 或者 newString = newString + str[i]; } 
// 第三步：返回反轉(zhuǎn)的字符串 return newString; }reverseString('hello'); 
// => // "olleh"

function reverseString (str) {
 var newString = '';
 var i = str.length; while (i > 0) {
 newString += str.substring(i - 1, i);
 i--; 
} 
return newString;}reverseString("hello"); 
// => olleh

var str = "abcdefghij";
console.log("(1,2): " + str.substr(1,2));
 // (1,2): bcconsole.log("(-3,2): " + str.substr(-3,2));
 // (-3,2): hiconsole.log("(-3): " + str.substr(-3)); 
// (-3): hijconsole.log("(1): " + str.substr(1)); 
// (1): bcdefghijconsole.log("(-20, 2): " + str.substr(-20,2)); 
// (-20, 2): abconsole.log("(20, 2): " + str.substr(20,2)); 
// (20, 2):

var anyString = "Brave new world";
console.log("The character at index 0 is '" + anyString.charAt(0) + "'"); 
// =>The character at index 0 is 'B'console.log("The character at index 1 is '" + anyString.charAt(1) + "'"); 
// =>The character at index 1 is 'r'console.log("The character at index 2 is '" + anyString.charAt(2) + "'"); 
// =>The character at index 2 is 'a'console.log("The character at index 3 is '" + anyString.charAt(3) + "'"); 
// => The character at index 3 is 'v'console.log("The character at index 4 is '" + anyString.charAt(4) + "'"); 
// => The character at index 4 is 'e'console.log("The character at index 999 is '" + anyString.charAt(999) + "'"); 
// => The character at index 999 is ''

function reverseString(str) { if (str === "") { 
return ""; } else { 
return reverseString(str.substr(1)) + str.charAt(0); }
}reverseString("hello"); 
// => olleh

function reverseString(str) { 
return (str === '') ? '' : reverseString(str.substr(1)) + str.charAt(0);}
reverseString("hello"); 
// => olleh

function reverseString(str) { 
return str && reverseString(str.substr(1)) + str[0];
}reverseString("hello");
 // => olleh