String Basics and Memory Representation in DSA Javascript - Build from Scratch

String Basics and Memory Representation

📖 Scenario: Imagine you are working on a simple text editor that needs to handle and display user input strings correctly. Understanding how strings are stored and manipulated in memory helps you manage text efficiently.

🎯 Goal: You will create a string variable, check its length, access characters by index, and finally print the string and its length to understand how strings work in memory.

📋 What You'll Learn

Create a string variable with exact text

Create a variable to store the string length

Access a specific character in the string by index

Print the string and its length

💡 Why This Matters

🌍 Real World

Text editors, chat apps, and websites all use strings to store and display text. Understanding string basics helps in handling user input and displaying messages.

💼 Career

Many programming jobs require working with strings for data processing, user interfaces, and communication between systems.

1

Create a string variable

Create a string variable called text and set it to the exact value "Hello, World!".

DSA Javascript

// Create a string variable called text with value "Hello, World!"
// Your code here

Hint

Use const to create a variable and assign the string exactly as shown.

2

Find the length of the string

Create a variable called length and set it to the length of the string text using the .length property.

DSA Javascript

const text = "Hello, World!";
// Create a variable called length and assign it the length of text
// Your code here

Hint

Use text.length to get the number of characters in the string.

3

Access a character by index

Create a variable called firstChar and set it to the first character of text using index 0.

DSA Javascript

const text = "Hello, World!";
const length = text.length;
// Create a variable called firstChar and assign it the first character of text
// Your code here

Hint

Use square brackets [] with index 0 to get the first character.

4

Print the string and its length

Print the string text and the length length using two separate console.log statements.

DSA Javascript

const text = "Hello, World!";
const length = text.length;
const firstChar = text[0];
// Print text and length using console.log
// Your code here

Hint

Use console.log(text) and console.log(length) to print the values.

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