Function parameters in Javascript

Introduction

Function parameters let you give information to a function so it can work with different values.

When you want a function to add two numbers you give it the numbers as parameters.

When you want to greet different people, you pass their names as parameters.

When you want to calculate the area of different rectangles, you pass width and height as parameters.

Syntax

Javascript

function functionName(parameter1, parameter2) {
  // code using parameters
}

Parameters are like placeholders for values you give when calling the function.

You can have as many parameters as you need, separated by commas.

Examples

This function takes one parameter name and prints a greeting.

Javascript

function greet(name) {
  console.log('Hello, ' + name + '!');
}

This function takes two parameters and returns their sum.

Javascript

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

This function has no parameters and always says hello the same way.

Javascript

function sayHello() {
  console.log('Hello!');
}

Sample Program

This program defines a function that multiplies two numbers given as parameters and prints the result.

Javascript

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

const result = multiply(4, 5);
console.log('4 times 5 is', result);

Important Notes

If you call a function without enough parameters, the missing ones become undefined.

You can give default values to parameters to avoid undefined.

Parameters help make functions reusable with different inputs.

Summary

Function parameters let you send information into functions.

They act like variables inside the function holding the input values.

Using parameters makes your functions flexible and reusable.

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