I'm getting the following error:

cannot read property 'split' of undefined

However the array variable with the split method attached is correctly defined in the previous code line.

function findLongestWord(str) {

  for (i = 0; i < str.length; i++) {
    var array = str.split(" ");
    array[i].split("");
  }
}

findLongestWord("The quick brown fox jumped over the lazy dog");

I'm getting the following error:

cannot read property 'split' of undefined

However the array variable with the split method attached is correctly defined in the previous code line.

function findLongestWord(str) {

  for (i = 0; i < str.length; i++) {
    var array = str.split(" ");
    array[i].split("");
  }
}

findLongestWord("The quick brown fox jumped over the lazy dog");

• javascript
• arrays
• function
• for-loop
• split

• 3 Do you want to iterate over each word, or do you want to iterate over each character? Figure that out, and then you can figure out which line you need to remove – CertainPerformance Commented Apr 20, 2018 at 9:51
• 1 what is your expected output ? – Muhammad Usman Commented Apr 20, 2018 at 9:52
• 3 str.length is 44. array has 9 elements. What do you think happens when you access array[10]? – Ivar Commented Apr 20, 2018 at 9:52
• 2 Possible duplicate of Javascript: find longest word in a string – Durga Commented Apr 20, 2018 at 9:54

3 Answers 3

str.length is actually the number of letters in the string, while array is an array of words. That's why i can go up to 45, while your array has only 9 elements - that's why when it tries to access array[10] it gets undefined and it can't split it. This should help:

function findLongestWord(str) {
  var array = str.split(" ");
  for (i = 0; i < array.length; i++) {
    array[i].split("");
  }
}

findLongestWord("The quick brown fox jumped over the lazy dog");

If you want it to actually return the longest word, you need to do something like this:

function findLongestWord(str) {
  var longestWord = ""
  var array = str.split(" ");
  for (i = 0; i < array.length; i++) {
    if(array[i].length > longestWord.length){
      longestWord = array[i]
    }
  }
  return longestWord
}

findLongestWord("The quick brown fox jumped over the lazy dog");

str.length get the length of the string counting chars, so 44, then you do the split by spaces, so you get the words but you continue to call index of each char in the string, to get longest word instead of:

array[i].split("");

you must do:

var longest = "";
array.forEach(function(word) {
    if(word.length > longest.length) {
      longest = word;
    }
});

You can directly apply split(" ") and use reduce() method of array to get required result.

The reduce() method applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.

DEMO

const str = "The quick brown fox jumped over the lazy dog";

let result = str.split(" ").reduce((r, v) => r.length > v.length ? r : v, '');

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }