Javascript：将.sort与compare函数结合使用以查找数组中最长的单词

Question

I am a beginner student in Javascript. I have been puzzling over this problem for the last few hours, so I'm hoping that somebody can help me with the the logic in the code I'm trying to write.

I am currently trying to write a function that will take the longest string in an array and pass it back to the console. If there is a tie, the console should return the first word with the most letters.

I found a good piece of code that will do this, but I can't find a way to make it into a function.

arr. sort(function (a, b) { return b.length - a.length })[0];

I tried

var longestWord = function(arr) {
    sort(function (a, b) { return b.length - a.length })[0];
}

This doesn't work. I know I'm doing something wrong, but I'm not sure what it is. Also, I can't quite grasp why exactly this words. I can can understand that the function compares the lengths of the two variables, but why does the 0 index have to be at the end?

Any help is greatly appreciated!!

Answer 1

Your function returns nothing. Also, you call sort function, but not Array.prototype.sort .

This one does work:

 var longestWord = function(arr) { return arr.sort(function (a, b) { return b.length - a.length })[0]; } document.body.innerText = longestWord(['a', 'ab', 'abcdef', 'abcd', 'a', 'abcde']); // abcdef 

Answering your "but why does the 0 index have to be at the end" question: Array.prototype.sort returns an array, and you get the first item in an array in order to get the longest word. This [0] is an array subscript, ie "first item in an array".

These two snippets are equivalent :

var arr = ['a', 'ab', 'abcdef', 'abcd', 'a', 'abcde']; 
// arr is ['a', 'ab', 'abcdef', 'abcd', 'a', 'abcde']

var arrSorted = arr.sort(function(a, b) { return b.length - a.length; });
// arrSorted is ['abcdef', 'abcde', 'abcd', 'ab', 'a', 'a']

var result = arrSorted[0];
// result is abcdef, the longest word

and

var arr = ['a', 'ab', 'abcdef', 'abcd', 'a', 'abcde']; 
// arr is ['a', 'ab', 'abcdef', 'abcd', 'a', 'abcde']

var result = arr.sort(function(a, b) { return b.length - a.length; })[0];
// result is abcdef, the longest word

The difference is that the second one doesn't store the intermediate result in a variable.

Answer 2

var my_array = ["a", "aaa", "aa", "aaaaaaa", "a"];
function longestString(arr) {
  return arr.sort(function(a,b) {
    return b.length - a.length;
  })[0];
}
longestString(my_array);

I would suggest use to read this https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort before you use sort(). Make sure you understand the irator before using it.