Writing first JavaScript program - Mini Project: Build & Apply

Writing first JavaScript program

📖 Scenario: You want to create a simple program that greets a user by name. This is like saying hello to a friend when you meet them.

🎯 Goal: Build a JavaScript program that stores a name, creates a greeting message using that name, and then shows the greeting on the screen.

📋 What You'll Learn

Create a variable to store a name

Create a variable to store a greeting message using the name

Display the greeting message using console.log

💡 Why This Matters

🌍 Real World

Greeting users by name is common in websites and apps to make them feel welcome.

💼 Career

Knowing how to create variables, use strings, and display output is the foundation of programming in JavaScript.

1

Create a variable with a name

Create a variable called userName and set it to the string "Alice".

Javascript

// Your code here
// Create a variable called userName and set it to "Alice"

Hint

Use const to create a variable and assign the value "Alice" to userName.

2

Create a greeting message

Create a variable called greeting and set it to the string `Hello, ${userName}!` using a template literal.

Javascript

const userName = "Alice";
// Your code here
// Create a variable called greeting using a template literal with userName

Hint

Use backticks ` and ${} to insert the variable userName inside the string.

3

Display the greeting message

Use console.log to display the value of the variable greeting.

Javascript

const userName = "Alice";
const greeting = `Hello, ${userName}!`;
// Your code here
// Use console.log to show greeting

Hint

Use console.log(greeting); to print the greeting message to the console.

4

Run the program to see the greeting

Run the program and make sure the output is exactly Hello, Alice!.

Javascript

const userName = "Alice";
const greeting = `Hello, ${userName}!`;
console.log(greeting);
// Run the program to see the output

Hint

Check the console output to see the greeting message.

Practice

1. What does the console.log() function do in JavaScript?

easy

A. It changes the background color of the page.

B. It creates a pop-up alert on the screen.

C. It stops the program from running.

D. It shows messages in the browser console.

Solution

1. Step 1: Understand the purpose of console.log()

   This function is used to display messages or values in the browser's console, which helps developers see output or debug.

2. Step 2: Compare with other options

   Options A, B, and D describe different actions that console.log() does not perform.

3. Final Answer:

   It shows messages in the browser console. -> Option D

4. Quick Check:

   console.log() shows messages [OK]

Hint: Remember: console.log prints messages to the console [OK]

Common Mistakes:

• Thinking console.log creates alerts
• Confusing console.log with styling commands
• Assuming console.log stops the program

2. Which of the following is the correct syntax to print "Hello, World!" in JavaScript?

easy

A. print("Hello, World!");

B. console.log("Hello, World!");

C. echo "Hello, World!";

D. System.out.println("Hello, World!");

Solution

1. Step 1: Identify JavaScript syntax for output

   JavaScript uses console.log() to print messages to the console.

2. Step 2: Check other options for language mismatch

   A is Python style, B is Java style, C is PHP style, so they are incorrect for JavaScript.

3. Final Answer:

   console.log("Hello, World!"); -> Option B

4. Quick Check:

   JavaScript output uses console.log() [OK]

Hint: Use console.log() to print messages in JavaScript [OK]

Common Mistakes:

• Using print() instead of console.log()
• Confusing JavaScript with other languages
• Missing parentheses or semicolon

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

console.log('Hi');
console.log('There');

medium

A. Hi
There

B. Hi There

C. Hi\nThere

D. HiThere

Solution

1. Step 1: Understand console.log behavior

   Each console.log() prints its message on a new line in the console.

2. Step 2: Analyze the output lines

   The first prints "Hi", then the second prints "There" on the next line, so output is two lines: "Hi" then "There".

3. Final Answer:

   Hi There -> Option A

4. Quick Check:

   console.log prints each message on a new line [OK]

Hint: Each console.log prints on a new line automatically [OK]

Common Mistakes:

• Thinking console.log joins messages on one line
• Confusing \n as literal text instead of newline
• Ignoring line breaks between calls

4. Find the error in this JavaScript code:

console.log('Hello World')

medium

A. console.log is misspelled

B. Incorrect quotes used

C. No error, code is correct

D. Missing semicolon at the end

Solution

1. Step 1: Check syntax correctness

   The code uses correct function name, quotes, and parentheses.

2. Step 2: Consider JavaScript semicolon rules

   Semicolons are optional at the end of statements in JavaScript, so missing semicolon is not an error.

3. Final Answer:

   No error, code is correct -> Option C

4. Quick Check:

   JavaScript allows optional semicolons [OK]

Hint: Semicolons are optional but recommended; no error here [OK]

Common Mistakes:

• Thinking missing semicolon causes error
• Confusing quote types as error
• Assuming console.log is misspelled

5. You want to write a JavaScript program that prints your name and age on separate lines. Which code will do this correctly?

hard

A. console.log('Name: John'); console.log('Age: 25');

B. console.log('Name: John\nAge: 25');

C. console.log('Name: John' + 'Age: 25');

D. console.log('Name: John Age: 25');

Solution

1. Step 1: Understand printing on separate lines

   Using two console.log() calls prints each message on its own line.

2. Step 2: Check other options for line breaks

   console.log('Name: John\nAge: 25'); uses \n which creates a newline in the output; console.log('Name: John' + 'Age: 25'); joins to 'Name: JohnAge: 25' on one line; console.log('Name: John Age: 25'); prints all on one line.

3. Final Answer:

   console.log('Name: John'); console.log('Age: 25'); -> Option A

4. Quick Check:

   Separate console.log calls print on separate lines [OK]

Hint: Use separate console.log() for each line [OK]

Common Mistakes:

• Using + without spaces causing joined text
• Thinking \n creates a newline (prints literal \n)
• Printing all info in one console.log without breaks