Cannot Read Property of Undefined Mocha React

If yous've ever used JavaScript's split method, there'south a good risk that you've encountered the following mistake: TypeError: Cannot read holding 'split' of undefined.

There are a few reasons why yous would receive this error. Most likely it'south just a bones misunderstanding of how split works and how to iterate through arrays.

For example, if you effort to submit the following code for the Find the Longest Word in a String challenge:

                function findLongestWord(str) {    for(let i = 0; i < str.length; i++) {     const array = str.split up(" ");     assortment[i].separate("");   } }  findLongestWord("The quick brown play a joke on jumped over the lazy dog");              

it will throw the TypeError: Cannot read belongings 'separate' of undefined error.

The separate method

When split is chosen on a cord, it splits the string into substrings based on the separator passed in as an argument. If an empty string is passed equally an argument, divide treats each graphic symbol as a substring. It then returns an assortment containing the substrings:

                const testStr1 = "Test test 1 2"; const testStr2 = "cupcake pancake"; const testStr3 = "First,2d,Tertiary";  testStr1.split(" "); // [ 'Test', 'exam', '1', 'two' ] testStr2.separate(""); // [ 'c', 'u', 'p', 'c', 'a', 'thou', 'e', ' ', 'p', 'a', 'due north', 'c', 'a', 'k', 'due east' ] testStr3.split(","); // [ 'First', 'Second', 'Third' ]                              

Check out MDN for more than details well-nigh separate.

The trouble explained with examples

Knowing what the split up method returns and how many substrings you lot can expect is the cardinal to solving this challenge.

Allow's take another look at the code above and see why information technology's not working as expected:

                function findLongestWord(str) {    for(permit i = 0; i < str.length; i++) {     const array = str.split(" ");     array[i].split("");   } }  findLongestWord("The quick dark-brown fox jumped over the lazy dog");                              

Splitting str into an assortment similar this (const array = str.split(" ");) works every bit expected and returns [ 'The',   'quick',   'brown',   'fox',   'jumped',   'over',   'the',   'lazy',   'canis familiaris' ].

Only have a closer look at the for loop. Rather than using the length of array as a status to iterate i, str.length is used instead.

str is "The quick chocolate-brown fox jumped over the lazy dog", and if you lot log str.length to the console, y'all'll get 44.

The last argument in the torso of the for loop is what's causing the mistake: assortment[i].carve up("");. The length of array is 9, so i would quickly go way over the maximum length of array:

                function findLongestWord(str) {    for(let i = 0; i < str.length; i++) {     const array = str.divide(" ");     console.log(array[i]);     // array[0]: "The"     // array[1]: "quick"     // array[2]: "brown"     // ...     // array[9]: "dog"     // assortment[ten]: undefined     // array[11]: undefined   } }  findLongestWord("The quick brown play tricks jumped over the lazy dog");                              

Calling array[i].split(""); to split each cord into substrings of characters is a valid approach, only it will throw TypeError: Cannot read property 'divide' of undefined when it's passed undefined.

How to solve Find the Longest Word in a String with split

Allow's quickly become over some pseudo code for how to solve this problem:

1. Separate str into an assortment of individual words
2. Create a variable to runway the greatest give-and-take length
3. Iterate through the assortment of words and compare the length of each discussion to the variable mentioned above
4. If the length of the current word is greater than the 1 stored in the variable, replace that value with the electric current word length
5. Once the length of every give-and-take is compared with the maximum word length variable, return that number from the part

First, split str into an array of private words:

                function findLongestWordLength(str) {   const array = str.split(" "); }              

Create a variable to keep track of the longest word length and prepare information technology to nix:

                function findLongestWordLength(str) {   const assortment = str.split(" ");   let maxWordLength = 0; }              

Now that the value of array is ['The', 'quick', 'brownish', 'fob', 'jumped', 'over', 'the', 'lazy', 'domestic dog'], you can apply array.length in your for loop:

                office findLongestWordLength(str) {   const array = str.split up(" ");   let maxWordLength = 0;      for (permit i = 0; i < array.length; i++) {        } }              

Iterate through the assortment of words and bank check the length of each word. Think that strings also have a length method you can call to easily get the length of a string:

                function findLongestWordLength(str) {   const array = str.divide(" ");   let maxLength = 0;      for (let i = 0; i < assortment.length; i++) {     assortment[i].length;   } }              

Use an if statement check if the length of the electric current give-and-take (array[i].length) is greater than maxLength. If and so, supplant the value of maxLength with array[i].length:

                function findLongestWordLength(str) {   const assortment = str.split(" ");   allow maxLength = 0;      for (let i = 0; i < array.length; i++) {     if (array[i].length > maxLength) {       maxLength = array[i].length;     }   } }              

Finally, return maxLength at the stop of the function, afterward the for loop:

                function findLongestWordLength(str) {   const array = str.dissever(" ");   let maxLength = 0;      for (let i = 0; i < array.length; i++) {     if (array[i].length > maxLength) {       maxLength = array[i].length;     }   }        return maxLength; }              

---

Learn to code for free. freeCodeCamp'southward open source curriculum has helped more than 40,000 people become jobs as developers. Get started

weberentrught1943.blogspot.com

Source: https://www.freecodecamp.org/news/cannot-read-property-split-of-undefined-error/

Share this post