String type behavior in Typescript - Mini Project: Build & Apply

String type behavior

📖 Scenario: Imagine you are working on a simple program that handles names of fruits. You want to learn how strings work in TypeScript by creating and manipulating string variables.

🎯 Goal: You will create a string variable, add another string to it, and then display the final combined string.

📋 What You'll Learn

Create a string variable with a specific value

Create another string variable to add

Combine the two strings using the + operator

Print the combined string

💡 Why This Matters

🌍 Real World

Handling and combining text data is common in many programs, like showing names, messages, or labels.

💼 Career

Understanding string behavior is essential for any programming job that involves user input, display, or text processing.

1

Create a string variable

Create a string variable called fruit and set it to the value "Apple".

Typescript

# Your code here

Hint

Use let to declare a variable and set its type to string.

2

Create another string variable

Create another string variable called moreFruit and set it to the value " Banana" (note the space before Banana).

Typescript

let fruit: string = "Apple";
# Your code here

Hint

Remember to include the space before Banana so the words separate when combined.

3

Combine the two strings

Create a new string variable called allFruits that combines fruit and moreFruit using the + operator.

Typescript

let fruit: string = "Apple";
let moreFruit: string = " Banana";
# Your code here

Hint

Use the + operator to join two strings.

4

Print the combined string

Use console.log to print the value of allFruits.

Typescript

let fruit: string = "Apple";
let moreFruit: string = " Banana";
let allFruits: string = fruit + moreFruit;
# Your code here

Hint

Use console.log(allFruits); to show the combined string in the console.

Practice

1. Which of the following is the correct way to declare a string variable in TypeScript?

easy

A. let name: string = "Alice";

B. let name = 123;

C. let name: number = "Alice";

D. let name: boolean = true;

Solution

1. Step 1: Understand TypeScript string type declaration

   In TypeScript, to declare a string variable, use let variableName: string = value; where value is text in quotes.

2. Step 2: Check each option's type and value

   let name: string = "Alice"; uses string type and assigns a text value "Alice" correctly. Others assign wrong types or values.

3. Final Answer:

   let name: string = "Alice"; -> Option A

4. Quick Check:

   Correct string declaration = let name: string = "Alice"; [OK]

Hint: String variables use : string and quotes [OK]

Common Mistakes:

• Assigning number or boolean to string type
• Missing type annotation when required
• Using wrong quotes for strings

2. Which of the following is the correct syntax to create a template string in TypeScript?

easy

A. let greeting = `Hello, ${name}!`;

B. let greeting = Hello, ${name}!;

C. let greeting = "Hello, ${name}!";

D. let greeting = 'Hello, ${name}!';

Solution

1. Step 1: Identify template string syntax

   Template strings use backticks ` and allow embedding variables with ${variable}.

2. Step 2: Check each option's quotes and variable embedding

   let greeting = `Hello, ${name}!`; correctly uses backticks and ${name} syntax. Options A and C use single or double quotes which do not support variable embedding. let greeting = Hello, ${name}!; misses quotes entirely.

3. Final Answer:

   let greeting = `Hello, ${name}!`; -> Option A

4. Quick Check:

   Template strings use backticks = let greeting = `Hello, ${name}!`; [OK]

Hint: Use backticks ` for template strings with ${} [OK]

Common Mistakes:

• Using single or double quotes for templates
• Forgetting backticks
• Not wrapping string in quotes

3. What is the output of the following TypeScript code?

const text: string = "Hello World";
console.log(text.length);

medium

A. 10

B. 11

C. 12

D. Error

Solution

1. Step 1: Understand string length property

   The length property returns the number of characters in the string, including spaces.

2. Step 2: Count characters in "Hello World"

   "Hello World" has 11 characters: 5 letters + 1 space + 5 letters.

3. Final Answer:

   11 -> Option B

4. Quick Check:

   "Hello World" length = 11 [OK]

Hint: Count all characters including spaces for length [OK]

Common Mistakes:

• Ignoring spaces in length count
• Confusing length with last index
• Expecting syntax error

4. Identify the error in this TypeScript code snippet:

let message: string = 'Hello';
message.toUppercase();

medium

A. Strings do not have toUpperCase method

B. No error, outputs 'HELLO'

C. Method name should be toUpperCase() with capital C

D. Missing semicolon after string declaration

Solution

1. Step 1: Check method name spelling

   The correct method to convert string to uppercase is toUpperCase() with capital 'C'.

2. Step 2: Identify error cause

   Using toUppercase() (lowercase 'c') causes a runtime error because the method does not exist.

3. Final Answer:

   Method name should be toUpperCase() with capital C -> Option C

4. Quick Check:

   Correct method spelling = Method name should be toUpperCase() with capital C [OK]

Hint: Remember uppercase C in toUpperCase() method [OK]

Common Mistakes:

• Using wrong case in method names
• Assuming strings lack case methods
• Ignoring runtime errors

5. Given the following code, what does this code check?

const name: string = "Anna";
const reversed = name.split("").reverse().join("");
console.log(reversed === name);

hard

A. If the string length is even

B. If the string is empty

C. If the string contains only letters

D. If the string is a palindrome (same forwards and backwards)

Solution

1. Step 1: Understand string reversal steps

   The code splits the string into characters, reverses the array, then joins back to a string.

2. Step 2: Compare reversed string with original

   It checks if the reversed string equals the original string, which means the string reads the same forwards and backwards.

3. Final Answer:

   If the string is a palindrome (same forwards and backwards) -> Option D

4. Quick Check:

   Reversed equals original means palindrome = If the string is a palindrome (same forwards and backwards) [OK]

Hint: Reversing and comparing checks palindrome [OK]

Common Mistakes:

• Confusing palindrome with empty string
• Thinking it checks string length or letters
• Missing split-reverse-join logic