How Strings Work Differently Across Languages in DSA Javascript - Code Step by Step

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];

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

Asize

Blength

Ccount

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'len' like in Python

Trying to call length as a function

In JavaScript, strings have a length property to get their size.

2fill in blank

medium

Complete the code to get the character at index 2.

DSA Javascript

const str = 'world';
const char = str.[1](2);

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

AcharAt

BgetChar

CcharCodeAt

Dsubstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'getChar' which doesn't exist

Using 'charCodeAt' which returns a number

The charAt() method returns the character at a given index in a string.

3fill in blank

hard

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

DSA Javascript

const str = 'hello';
const upper = str.[1]();

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

AupperCase

Buppercase

CtoUpperCase

DtoUppercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'toUppercase' with lowercase 'c'

Using 'uppercase' which is not a method

The correct method name is toUpperCase() with a capital 'C'.

4fill in blank

hard

Fill both blanks to extract 'cat' from the string.

DSA Javascript

const str = 'concatenate';
const part = str.[1](3, [2]);

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

Asubstring

Bsubstr

C7

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using substr with wrong length

Confusing substring end index as inclusive

The substring(3, 6) extracts characters from index 3 up to but not including index 6: 'c' (3), 'a' (4), 't' (5) = 'cat'.

5fill in blank

hard

Fill all three blanks to create a new string with 'Hello World!' in uppercase.

DSA Javascript

const greeting = '[1]' + ' ' + '[2]' + '[3]';
const shout = greeting.toUpperCase();

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

AHello

BWorld

C!

Dworld

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'world'

Missing the exclamation mark

Concatenate 'Hello', 'World', and '!' with spaces to form 'Hello World!'. Then convert to uppercase.

Practice

1. In JavaScript, which of the following statements about strings is true?

easy

A. Strings are immutable, meaning you cannot change a character directly.

B. Strings are mutable, so you can change characters by index.

C. Strings are stored as arrays of characters that can be modified.

D. Strings are objects that allow direct character assignment.

Solution

1. Step 1: Understand string mutability in JavaScript

   JavaScript strings cannot be changed after creation; they are immutable.

2. Step 2: Compare with other options

   Options A, B, and C suggest mutability or direct modification, which is incorrect.

3. Final Answer:

   Strings are immutable, meaning you cannot change a character directly. -> Option A

4. Quick Check:

   JavaScript strings are immutable = D [OK]

Hint: Remember: JavaScript strings cannot be changed character by character [OK]

Common Mistakes:

• Thinking strings behave like arrays and can be changed by index
• Confusing string immutability with array mutability
• Assuming strings are objects with mutable properties

2. Which of the following is the correct way to get the length of a string str in JavaScript?

easy

A. str.size

B. str.length()

C. length(str)

D. str.length

Solution

1. Step 1: Recall JavaScript string length syntax

   In JavaScript, string length is accessed as a property without parentheses: str.length

2. Step 2: Check other options for syntax errors

   str.length() uses parentheses which is incorrect; C and D are not valid JavaScript syntax for string length.

3. Final Answer:

   str.length -> Option D

4. Quick Check:

   Use property .length without () = A [OK]

Hint: Use .length property without parentheses for string length [OK]

Common Mistakes:

• Using parentheses like a function call (str.length())
• Confusing with other languages that use length() function
• Trying to use str.size which is invalid in JavaScript

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

const s = 'hello';
console.log(s[1]);
s[1] = 'a';
console.log(s[1]);

medium

A. e\ne

B. e\na

C. undefined\na

D. undefined\ne

Solution

1. Step 1: Check first console.log(s[1])

   Index 1 of 'hello' is 'e', so first output is 'e'.

2. Step 2: Attempt to change s[1] and check second console.log(s[1])

   Strings are immutable, so s[1] = 'a' does nothing; second output remains 'e'.

3. Final Answer:

   e\ne -> Option A

4. Quick Check:

   Immutable strings keep original chars = B [OK]

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

Common Mistakes:

• Expecting s[1] to change to 'a'
• Confusing string mutability with arrays
• Assuming assignment to string index works

4. Identify the error in the following JavaScript code snippet:

let str = 'world';
str[0] = 'W';
console.log(str);

medium

A. No error; output is 'World'

B. No error; output is 'world'

C. TypeError because strings are immutable

D. SyntaxError due to invalid assignment

Solution

1. Step 1: Understand string immutability and assignment

   Assigning to str[0] does not change the string; no error is thrown.

2. Step 2: Check console.log output

   Since assignment fails silently, output remains original string 'world'.

3. Final Answer:

   No error; output is 'world' -> Option B

4. Quick Check:

   Immutable strings ignore index assignment = C [OK]

Hint: Index assignment on strings fails silently, no error thrown [OK]

Common Mistakes:

• Expecting a TypeError on index assignment
• Thinking string changes after index assignment
• Confusing with languages that allow mutable strings

5. You want to replace the first character of a string str with an uppercase letter in JavaScript. Which approach correctly achieves this?

hard

A. str.replace(0, str[0].toUpperCase());

B. str[0] = str[0].toUpperCase();

C. str = str[0].toUpperCase() + str.slice(1);

D. str.toUpperCase()[0] + str.slice(1);

Solution

1. Step 1: Understand string immutability and modification

   Direct assignment to str[0] is invalid; strings are immutable.

2. Step 2: Check each option for correct string replacement

   str = str[0].toUpperCase() + str.slice(1); creates a new string by uppercasing first char and adding rest; this works correctly.

3. Step 3: Analyze other options

   B tries direct assignment (invalid), C uses replace incorrectly (replace needs substring, not index), D uppercases whole string then concatenates first char with rest but doesn't reassign to str (str unchanged).

4. Final Answer:

   str = str[0].toUpperCase() + str.slice(1); -> Option C

5. Quick Check:

   Use new string with uppercase first char + rest = A [OK]

Hint: Build new string; can't change characters directly [OK]

Common Mistakes:

• Trying to assign directly to str[0]
• Using replace with index instead of substring
• Uppercasing whole string instead of first char only