本文详解JavaScript中查找字符串最长单词的三种算法。通过For循环遍历比较长度、利用Sort方法排序后取首元素、以及使用Reduce方法累积最大值，分别展示具体实现逻辑与代码示例，帮助开发者掌握字符串处理与数组高阶函数的应用。
算法挑战背景与要求
本文内容源自Free Code Camp的基础算法脚本挑战，主题为“查找字符串中最长的单词”。
该算法的核心逻辑是遍历字符串中的每个单词，统计其字符数量，通过比较各单词的长度来确定最大值，最终返回最长单词的字符数。
本文将依次介绍三种实现方案：第一种基于For循环，第二种利用Sort方法，第三种采用Reduce方法。
算法挑战要求：
- 返回给定句子中最长单词的长度。
- 函数返回值必须为数字类型。
以下是提供的测试用例：
- findLongestWord("The quick brown fox jumped over the lazy dog") 应返回一个数字
- findLongestWord("The quick brown fox jumped over the lazy dog") 预期结果为6
- findLongestWord("May the force be with you") 预期结果为5
- findLongestWord("Google do a barrel roll") 预期结果为6
- findLongestWord("What is the average airspeed velocity of an unladen swallow") 预期结果为8
- findLongestWord("What if we try a super-long word such as otorhinolaryngology") 预期结果为19
function findLongestWord(str) {
return str.length;
}
findLongestWord("The quick brown fox jumped over the lazy dog");方法一：For循环实现
1. 使用For循环查找最长单词
该方案首先调用String.prototype.split()方法处理字符串。
- split()方法通过指定的分隔符将字符串拆分为子串，并返回包含这些子串的数组。
在调用split()时，需在参数中传入空格字符。
var strSplit = “The quick brown fox jumped over the lazy dog”.split(‘ ‘);正确操作后，输出结果为包含各个单词的数组：
var strSplit = [“The”, “quick”, “brown”, “fox”, “jumped”, “over”, “the”, “lazy”, “dog”];若未在参数中指定空格，输出结果将变为包含单个字符的数组：
var strSplit =
[“T”, “h”, “e”, “ “, “q”, “u”, “i”, “c”, “k”, “ “, “b”, “r”, “o”, “w”, “n”, “ “, “f”, “o”, “x”, “ “, “j”, “u”, “m”, “p”, “e”, “d”, “ “, “o”, “v”, “e”, “r”, “ “, “t”, “h”, “e”, “ “, “l”, “a”, “z”, “y”, “ “, “d”, “o”, “g”];
function findLongestWord(str) {
// Step 1. Split the string into an array of strings
var strSplit = str.split(' ');
// var strSplit = "The quick brown fox jumped over the lazy dog".split(' ');
// var strSplit = ["The", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog"];
// Step 2. Initiate a variable that will hold the length of the longest word
var longestWord = 0;
// Step 3. Create the FOR loop
for(var i = 0; i < strSplit.length; i++){
if(strSplit[i].length > longestWord){ // If strSplit[i].length is greater than the word it is compared with...
longestWord = strSplit[i].length; // ...then longestWord takes this new value
}
}
/* Here strSplit.length = 9
For each iteration: i = ? i < strSplit.length? i++ if(strSplit[i].length > longestWord)? longestWord = strSplit[i].length
1st iteration: 0 yes 1 if("The".length > 0)? => if(3 > 0)? longestWord = 3
2nd iteration: 1 yes 2 if("quick".length > 3)? => if(5 > 3)? longestWord = 5
3rd iteration: 2 yes 3 if("brown".length > 5)? => if(5 > 5)? longestWord = 5
4th iteration: 3 yes 4 if("fox".length > 5)? => if(3 > 5)? longestWord = 5
5th iteration: 4 yes 5 if("jumped".length > 5)? => if(6 > 5)? longestWord = 6
6th iteration: 5 yes 6 if("over".length > 6)? => if(4 > 6)? longestWord = 6
7th iteration: 6 yes 7 if("the".length > 6)? => if(3 > 6)? longestWord = 6
8th iteration: 7 yes 8 if("lazy".length > 6)? => if(4 > 6)? longestWord = 6
9th iteration: 8 yes 9 if("dog".length > 6)? => if(3 > 6)? longestWord = 6
10th iteration: 9 no
End of the FOR Loop*/
//Step 4. Return the longest word
return longestWord; // 6
}
findLongestWord("The quick brown fox jumped over the lazy dog");完整代码如下（无注释版）：
function findLongestWord(str) {
var strSplit = str.split(' ');
var longestWord = 0;
for(var i = 0; i < strSplit.length; i++){
if(strSplit[i].length > longestWord){
longestWord = strSplit[i].length;
}
}
return longestWord;
}
findLongestWord("The quick brown fox jumped over the lazy dog");方法二：Sort排序实现
2. 使用Sort方法查找最长单词
该方案利用Array.prototype.sort()方法对数组进行排序，随后返回排序后数组第一个元素的长度。
- sort()方法会对数组元素进行原地排序并返回该数组。
若直接对数组进行默认排序：
var sortArray = [“The”, “quick”, “brown”, “fox”, “jumped”, “over”, “the”, “lazy”, “dog”].sort();输出结果如下：
var sortArray = [“The”, “brown”, “dog”, “fox”, “jumped”, “lazy”, “over”, “quick”, “the”];在Unicode编码中，数字排在在大写字母之前，而大写字母排在小写字母之前。
因此，我们需要自定义排序规则。
[].sort(function(firstElement, secondElement) { return secondElement.length — firstElement.length; })具体做法是比较数组中第二个元素与第一个元素的长度。
function findLongestWord(str) {
// Step 1. Split the string into an array of strings
var strSplit = str.split(' ');
// var strSplit = "The quick brown fox jumped over the lazy dog".split(' ');
// var strSplit = ["The", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog"];
// Step 2. Sort the elements in the array
var longestWord = strSplit.sort(function(a, b) {
return b.length - a.length;
});
/* Sorting process
a b b.length a.length var longestWord
"The" "quick" 5 3 ["quick", "The"]
"quick" "brown" 5 5 ["quick", "brown", "The"]
"brown" "fox" 3 5 ["quick", "brown", "The", "fox"]
"fox" "jumped" 6 3 ["jumped", quick", "brown", "The", "fox"]
"jumped" "over" 4 6 ["jumped", quick", "brown", "over", "The", "fox"]
"over" "the" 3 4 ["jumped", quick", "brown", "over", "The", "fox", "the"]
"the" "lazy" 4 3 ["jumped", quick", "brown", "over", "lazy", "The", "fox", "the"]
"lazy" "dog" 3 4 ["jumped", quick", "brown", "over", "lazy", "The", "fox", "the", "dog"]
*/
// Step 3. Return the length of the first element of the array
return longestWord[0].length; // var longestWord = ["jumped", "quick", "brown", "over", "lazy", "The", "fox", "the", "dog"];
// longestWord[0]="jumped" => jumped".length => 6
}
findLongestWord("The quick brown fox jumped over the lazy dog");完整代码如下（无注释版）：
function findLongestWord(str) {
var longestWord = str.split(' ').sort(function(a, b) { return b.length - a.length; });
return longestWord[0].length;
}
findLongestWord("The quick brown fox jumped over the lazy dog");方法三：Reduce归约实现
3. 使用Reduce方法查找最长单词
该方案利用Array.prototype.reduce()方法。
- reduce()方法接收一个回调函数，对数组的每个值（从左到右）执行该函数，最终将其归约为单个值。
reduce()会对数组中的每个元素执行一次回调函数。
可以提供一个初始值作为reduce的第二个参数，此处我们传入一个空字符串""。
[].reduce(function(previousValue, currentValue) {...}, “”);
function findLongestWord(str) {
// Step 1. Split the string into an array of strings
var strSplit = str.split(' ');
// var strSplit = "The quick brown fox jumped over the lazy dog".split(' ');
// var strSplit = ["The", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog"];
// Step 2. Use the reduce method
var longestWord = strSplit.reduce(function(longest, currentWord) {
if(currentWord.length > longest.length)
return currentWord;
else
return longest;
}, "");
/* Reduce process
currentWord longest currentWord.length longest.length if(currentWord.length > longest.length)? var longestWord
"The" "" 3 0 yes "The"
"quick" "The" 5 3 yes "quick"
"brown" "quick" 5 5 no "quick"
"fox" "quick" 3 5 no "quick"
"jumped" "quick" 6 5 yes "jumped"
"over" "jumped" 4 6 no "jumped"
"the" "jumped" 3 6 no "jumped"
"lazy" "jumped" 4 6 no "jumped"
"dog" "jumped" 3 6 no "jumped"
*/
// Step 3. Return the length of the longestWord
return longestWord.length; // var longestWord = "jumped"
// longestWord.length => "jumped".length => 6
}
findLongestWord("The quick brown fox jumped over the lazy dog");完整代码如下（无注释版）：
function findLongestWord(str) {
var longestWord = str.split(' ').reduce(function(longest, currentWord) {
return currentWord.length > longest.length ? currentWord : longest;
}, "");
return longestWord.length;
}
findLongestWord("The quick brown fox jumped over the lazy dog");以上介绍了在JavaScript中查找字符串最长单词的三种方法。更多关于JS查找字符串最长单词的内容，可参考本站往期文章或继续浏览后续相关文章，感谢支持。