Function parameters in Javascript - Mini Project: Build & Apply

Function parameters

📖 Scenario: You are creating a simple calculator that adds two numbers. You will write a function that takes two numbers as inputs and returns their sum.

🎯 Goal: Build a function called addNumbers that takes two parameters and returns their sum. Then call the function with specific numbers and display the result.

📋 What You'll Learn

Create a function named addNumbers with two parameters: num1 and num2

Inside the function, return the sum of num1 and num2

Call the function with the numbers 5 and 7

Print the result using console.log

💡 Why This Matters

🌍 Real World

Functions with parameters are used everywhere in programming to reuse code and perform tasks with different inputs.

💼 Career

Understanding how to write and use functions with parameters is essential for any programming job, as it helps build clean and efficient code.

1

Create the function skeleton

Write a function named addNumbers that takes two parameters called num1 and num2. For now, leave the function body empty.

Javascript

function addNumbers(num1, num2) {
  // Your code here
}

Hint

Use the function keyword followed by the function name and parentheses with parameters.

2

Add the return statement

Inside the addNumbers function, write a return statement that returns the sum of num1 and num2.

Javascript

function addNumbers(num1, num2) {
  // Your code here
}

Hint

Use return num1 + num2; to send back the sum.

3

Call the function with numbers

Create a variable called result and assign it the value returned by calling addNumbers with the numbers 5 and 7.

Javascript

function addNumbers(num1, num2) {
  return num1 + num2;
}

// Your code here

Hint

Use const result = addNumbers(5, 7); to call the function and save the answer.

4

Display the result

Use console.log to print the value of the variable result.

Javascript

function addNumbers(num1, num2) {
  return num1 + num2;
}

const result = addNumbers(5, 7);

// Your code here

Hint

Use console.log(result); to show the sum in the console.

Practice

1.

What is the purpose of function parameters in JavaScript?

Choose the best explanation.

easy

A. They make functions run faster.

B. They create new functions automatically.

C. They stop a function from running.

D. They allow you to send information into functions to use inside.

Solution

1. Step 1: Understand what parameters do

   Parameters let you pass values into a function so it can use them inside.

2. Step 2: Evaluate the options

   Only "They allow you to send information into functions to use inside." correctly explains this purpose. Others describe unrelated or incorrect effects.

3. Final Answer:

   They allow you to send information into functions to use inside. -> Option D

4. Quick Check:

   Function parameters = input values [OK]

Hint: Parameters are inputs to functions, like filling a form [OK]

Common Mistakes:

• Thinking parameters create functions
• Believing parameters stop functions
• Assuming parameters speed up functions

2.

Which of the following is the correct way to define a function with two parameters a and b in JavaScript?

function add(???) { return a + b; }

easy

A. (a, b)

B. a b

C. a, b

D. [a, b]

Solution

1. Step 1: Recall function parameter syntax

   Parameters are listed separated by commas inside the function parentheses.

2. Step 2: Identify the correct parameter list

   (a, b) correctly lists parameters as 'a, b' inside parentheses. 'a, b' without parentheses is invalid syntax. Extra parentheses inside parentheses are not used.

3. Final Answer:

   (a, b) -> Option A

4. Quick Check:

   Parameters separated by commas inside () [OK]

Hint: List parameters separated by commas inside function parentheses [OK]

Common Mistakes:

• Using spaces instead of commas
• Adding extra parentheses around parameters
• Using brackets instead of commas

3.

What will be the output of this code?

function greet(name) {
  return `Hello, ${name}!`;
}
console.log(greet('Alice'));

medium

A. "Hello, Alice!"

B. "Hello, name!"

C. undefined

D. Error

Solution

1. Step 1: Understand function call with argument

   The function greet is called with 'Alice' as the argument for parameter name.

2. Step 2: Evaluate template literal output

   The template string inserts the value of name, so it becomes 'Hello, Alice!'.

3. Final Answer:

   "Hello, Alice!" -> Option A

4. Quick Check:

   Parameter value replaces placeholder [OK]

Hint: Parameter value replaces variable inside template strings [OK]

Common Mistakes:

• Thinking parameter name is printed literally
• Expecting undefined if parameter not used
• Confusing string quotes in output

4.

Find the error in this function definition:

function multiply(x, y) {
  return x * y;
}
multiply(5);

What will happen when multiply(5) is called?

medium

A. Throws a syntax error

B. Returns 25

C. Returns NaN

D. Returns 5

Solution

1. Step 1: Check function call with missing argument

   The function multiply expects two parameters but is called with only one argument (5).

2. Step 2: Understand behavior of missing parameter

   The second parameter y is undefined, so x * y becomes 5 * undefined, which results in NaN (Not a Number).

3. Final Answer:

   Returns NaN -> Option C

4. Quick Check:

   Missing argument causes NaN in math operations [OK]

Hint: Missing parameters become undefined, causing NaN in math [OK]

Common Mistakes:

• Expecting default value 0 for missing parameters
• Thinking it throws an error
• Assuming multiply returns the single argument

5.

Consider this function that uses default parameters:

function calculateTotal(price, tax = 0.1, discount = 0) {
  return price + price * tax - discount;
}
console.log(calculateTotal(100, undefined, 5));

What is the output of the console.log statement?

hard

A. 95

B. 105

C. 105.5

D. 105.0

Solution

1. Step 1: Understand default parameters and call

   The function has tax default 0.1 and discount default 0. The call passes price=100, tax=undefined, discount=5.

2. Step 2: Evaluate how undefined affects default

   Passing undefined for tax triggers the default value 0.1 to be used.

3. Step 3: Calculate the total

   Total = 100 + 100 * 0.1 - 5 = 100 + 10 - 5 = 105.

4. Final Answer:

   105 -> Option B

5. Quick Check:

   Undefined triggers default parameter value [OK]

Hint: Passing undefined uses default parameter value [OK]

Common Mistakes:

• Thinking undefined overrides default with undefined
• Ignoring discount in calculation
• Confusing tax and discount values