Function parameters in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are function parameters in JavaScript?

Function parameters are names listed in a function definition. They act like placeholders for values that the function will receive when called.

beginner

How do you define a function with two parameters named a and b?

You write: <br><pre>function example(a, b) {<br>  // code here<br>}</pre>

intermediate

What happens if you call a function with fewer arguments than parameters?

The missing parameters get the value undefined. You can check for this inside the function to handle missing values.

intermediate

What is a default parameter value in JavaScript functions?

A default parameter value is a value assigned to a parameter in the function definition. It is used if no argument is passed for that parameter when the function is called.

beginner

How do you write a function with a default parameter value of 10 for parameter num?

You write: <br><pre>function example(num = 10) {<br>  // code here<br>}</pre>

What will be the value of b when calling function test(a, b) {} as test(5)?

A null

B 5

C undefined

D 0

If you call a function with fewer arguments than parameters, the missing parameters get the value undefined.

How do you assign a default value of 100 to a parameter x in a function?

A function f(x <- 100) {}

B function f(x: 100) {}

C function f(x == 100) {}

D function f(x = 100) {}

The correct syntax for default parameters in JavaScript is function f(x = 100) {}.

Which of the following is true about function parameters?

A Parameters are placeholders for values passed to functions.

B Parameters store the return value of a function.

C Parameters are only used outside the function.

D Parameters must always have default values.

Parameters are names used inside function definitions to receive values when the function is called.

What happens if you call a function with more arguments than parameters?

A It causes a syntax error.

B Extra arguments are ignored unless accessed via special objects.

C The function automatically creates new parameters.

D The function stops running.

Extra arguments are ignored by named parameters but can be accessed using the arguments object or rest parameters.

Which keyword is used to collect multiple function arguments into an array?

A rest parameter (...)

B spread operator (...)

C default parameter

D arguments

The rest parameter syntax ...name collects multiple arguments into an array.

Explain what function parameters are and how they work in JavaScript.

Think about how functions get information to work with.

Describe how to use default parameter values and why they are useful.

Consider what happens when a function is called without some arguments.

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