Why built-in methods are useful in Javascript - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert the string to uppercase using a built-in method.

Javascript

const word = 'hello';
const upperWord = word.[1]();
console.log(upperWord);

Drag options to blanks, or click blank then click option'

AtoLowerCase

BtoUpperCase

Ctrim

Dsplit

Attempts:

3 left

💡 Hint

Common Mistakes

Using toLowerCase() instead of toUpperCase()

Trying to use a method that doesn't change case

The toUpperCase() method converts all letters in a string to uppercase.

2fill in blank

medium

Complete the code to find the length of the array using a built-in property.

Javascript

const fruits = ['apple', 'banana', 'cherry'];
const count = fruits[1];
console.log(count);

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A.length()

B.size

C.length

D.count

Attempts:

3 left

💡 Hint

Common Mistakes

Using .length() with parentheses

Using .size or .count which are not valid for arrays

The length property gives the number of items in an array.

3fill in blank

hard

Fix the error in the code to join array elements into a string separated by commas.

Javascript

const colors = ['red', 'green', 'blue'];
const result = colors.[1](',');
console.log(result);

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Ajoin

Bsplit

Cconcat

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using split() which breaks strings into arrays

Using concat() which merges arrays but not with separators

The join() method combines array elements into a string with a specified separator.

4fill in blank

hard

Fill both blanks to create an object with keys as words and values as their lengths, only for words longer than 3 letters.

Javascript

const words = ['cat', 'elephant', 'dog', 'lion'];
const lengths = Object.fromEntries(words.filter(word => word.length > 3).map(word => [[1], [2]]));
console.log(lengths);

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Aword

Bword.length

Cword.length()

Dword.toString()

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.length() which is not a function

Using word.toString() which returns the word itself

Use word as the key and word.length as the value. word.length is a property, not a function.

5fill in blank

hard

Fill all three blanks to create a new array with uppercase words that have length greater than 3.

Javascript

const words = ['sun', 'moon', 'star', 'sky'];
const result = words.filter(word => word.[1] > [2]).map(word => word.[3]());
console.log(result);

Drag options to blanks, or click blank then click option'

Alength

B3

CtoUpperCase

DtoLowerCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using length() instead of length

Using toLowerCase() instead of toUpperCase()

Filter words with length greater than 3, then convert each to uppercase using toUpperCase().