String Basics and Memory Representation in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the length of the string.

DSA Javascript

const str = 'hello';
const length = str.[1];
console.log(length);

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

Alength

Bcount

Csize

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using len or size which are not valid for strings in JavaScript.

The length property returns the number of characters in a string in JavaScript.

2fill in blank

medium

Complete the code to access the first character of the string.

DSA Javascript

const word = 'world';
const firstChar = word[1];
console.log(firstChar);

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

A.0

B(0)

C[0]

D{0}

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or curly braces which are invalid for string indexing.

In JavaScript, strings can be accessed like arrays using square brackets [] with the index inside.

3fill in blank

hard

Fix the error in the code to convert the string to uppercase.

DSA Javascript

const text = 'hello';
const upper = text.[1]();
console.log(upper);

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

AtoUpper

BtoUpperCase

Cuppercase

Dtouppercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect casing like touppercase() or incomplete method names.

The correct method to convert a string to uppercase in JavaScript is toUpperCase() with exact casing.

4fill in blank

hard

Fill both blanks to create a new string by repeating 'ha' three times.

DSA Javascript

const laugh = 'ha'.[1]([2]);
console.log(laugh);

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

Arepeat

B3

C2

Dconcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using concat which joins strings but does not repeat.

The repeat() method repeats a string a specified number of times. Here, repeating 'ha' 3 times gives 'hahaha'.

5fill in blank

hard

Fill all three blanks to extract 'cat' from the string 'concatenate'.

DSA Javascript

const word = 'concatenate';
const part = word.[1]([2], [3]);
console.log(part);

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

Aslice

B3

C6

Dsubstr

Attempts:

3 left

💡 Hint

Common Mistakes

Using substr which takes start and length, not end index.

The slice(start, end) method extracts characters from start index up to but not including end. Here, slice(3, 6) extracts 'cat'.

Practice

1. What does the term immutable mean when talking about strings in JavaScript?

easy

A. Strings cannot be changed after they are created

B. Strings can be changed anytime

C. Strings are stored as numbers

D. Strings are always empty

Solution

1. Step 1: Understand string immutability

   In JavaScript, once a string is created, its content cannot be changed directly.

2. Step 2: Compare options with definition

   Strings cannot be changed after they are created - this matches the definition.

3. Final Answer:

   Strings cannot be changed after they are created -> Option A

4. Quick Check:

   Immutable means unchangeable = D [OK]

Hint: Remember: strings can't be changed once made [OK]

Common Mistakes:

• Thinking strings can be changed like arrays
• Confusing immutability with emptiness
• Assuming strings are stored as numbers

2. Which of the following is the correct way to create a string in JavaScript?

easy

A. const str = Hello World;

B. const str = (Hello World);

C. const str = `Hello World;

D. const str = 'Hello World';

Solution

1. Step 1: Check string syntax rules

   Strings must be enclosed in quotes: single (' '), double (" "), or backticks (` `).

2. Step 2: Validate each option

   const str = 'Hello World'; uses single quotes correctly. const str = Hello World; misses quotes. const str = `Hello World; misses closing backtick. const str = (Hello World); uses parentheses incorrectly.

3. Final Answer:

   const str = 'Hello World'; -> Option D

4. Quick Check:

   Quotes needed for strings = B [OK]

Hint: Strings need quotes around text [OK]

Common Mistakes:

• Forgetting quotes around string text
• Using mismatched or missing quotes
• Using parentheses instead of quotes

3. What will be the output of the following code?

let s = 'hello';
s[0] = 'H';
console.log(s);

medium

A. hello

B. Hello

C. undefined

D. Error

Solution

1. Step 1: Understand string immutability in code

   Strings cannot be changed by assigning to an index like s[0] = 'H'. This operation is ignored.

2. Step 2: Check what console.log prints

   The original string 'hello' remains unchanged and is printed.

3. Final Answer:

   hello -> Option A

4. Quick Check:

   Strings unchanged by index assignment = A [OK]

Hint: Strings ignore index assignment, original stays same [OK]

Common Mistakes:

• Expecting first letter to change
• Thinking strings behave like arrays
• Assuming error will be thrown

4. Find the error in this code snippet that tries to change a string character:

let word = 'code';
word[2] = 'd';
console.log(word);

medium

A. Variable word is not declared

B. Strings are immutable; cannot assign to index

C. Missing semicolon after declaration

D. console.log syntax is wrong

Solution

1. Step 1: Analyze string modification attempt

   Assigning to a string index like word[2] = 'd' does not change the string because strings are immutable.

2. Step 2: Check other options for errors

   Semicolons are optional in JavaScript, variable is declared, and console.log syntax is correct.

3. Final Answer:

   Strings are immutable; cannot assign to index -> Option B

4. Quick Check:

   Immutable strings block index assignment = C [OK]

Hint: Strings can't be changed by index assignment [OK]

Common Mistakes:

• Thinking semicolon is mandatory here
• Assuming variable is undeclared
• Believing console.log syntax is incorrect

5. Given the code below, what will be the output?

const str1 = 'abc';
const str2 = str1 + 'd';
console.log(str1);
console.log(str2);

Choose the correct output representation.

hard

A. Both lines print abcd

B. abcd and abc printed on separate lines

C. abc and abcd printed on separate lines

D. Error because strings are immutable

Solution

1. Step 1: Understand string concatenation and immutability

   str1 remains 'abc' because strings are immutable. str2 is a new string 'abcd' created by adding 'd' to str1.

2. Step 2: Check console.log outputs

   console.log(str1) prints abc. console.log(str2) prints abcd.

3. Final Answer:

   abc and abcd printed on separate lines -> Option C

4. Quick Check:

   Original unchanged, new string created = A [OK]

Hint: Concatenation creates new string, original stays same [OK]

Common Mistakes:

• Thinking original string changes after concatenation
• Expecting error due to immutability
• Confusing order of printed strings