Function execution flow in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the function greet.

Javascript

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

greet[1];

Drag options to blanks, or click blank then click option'

A[]

B{}

C()

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the parentheses and just writing the function name.

Using curly braces or square brackets instead of parentheses.

To execute a function in JavaScript, you add parentheses after its name, like greet().

2fill in blank

medium

Complete the code to return the sum of two numbers inside the function.

Javascript

function add(a, b) {
  return a [1] b;
}

Drag options to blanks, or click blank then click option'

A/

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction - instead of addition.

Using multiplication or division operators by mistake.

The plus sign + adds two numbers together in JavaScript.

3fill in blank

hard

Fix the error in the function call to correctly pass the argument.

Javascript

function sayName(name) {
  console.log('Name:', name);
}

sayName[1];

Drag options to blanks, or click blank then click option'

A'John'

B('John')

C(John)

DJohn

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the string without quotes, causing a reference error.

Not using parentheses to call the function.

When calling a function with a string argument, you must put the string in quotes inside parentheses, like sayName('John').

4fill in blank

hard

Fill both blanks to create a function that returns the square of a number.

Javascript

function square(num) {
  return num [1] [2];
}

Drag options to blanks, or click blank then click option'

A**

B*

C2

Dnum

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication * but forgetting to multiply by the number itself.

Using the wrong operator or missing the exponent.

The exponentiation operator ** raises a number to a power. To square a number, use num ** 2.

5fill in blank

hard

Fill the blanks to create a function that filters numbers greater than 10 from an array.

Javascript

function filterGreater(arr) {
  return arr.filter(num => num [1] [2]);
}

Drag options to blanks, or click blank then click option'

A>

B10

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality == instead of greater than.

Using less than < instead of greater than.

To filter numbers greater than 10, use the greater than operator > and compare with 10: num > 10.

Practice

1. What happens when a JavaScript function is defined but not called?

easy

A. The function runs twice.

B. The function code does not run.

C. The program crashes.

D. The function runs automatically once defined.

Solution

1. Step 1: Understand function definition

   Defining a function only tells the program what the function does but does not run it.

2. Step 2: Recognize function call requirement

   The function code runs only when the function is called explicitly.

3. Final Answer:

   The function code does not run. -> Option B

4. Quick Check:

   Function runs only when called [OK]

Hint: Functions run only when called, not when defined [OK]

Common Mistakes:

• Thinking function runs on definition
• Confusing declaration with execution
• Assuming automatic call

2. Which of the following is the correct way to call a function named greet in JavaScript?

easy

A. greet[];

B. call greet;

C. function greet();

D. greet();

Solution

1. Step 1: Identify function call syntax

   In JavaScript, calling a function requires its name followed by parentheses.

2. Step 2: Check each option

   greet(); uses greet(); which is correct. Others use invalid syntax.

3. Final Answer:

   greet(); -> Option D

4. Quick Check:

   Function call = name + () [OK]

Hint: Call functions with parentheses after name [OK]

Common Mistakes:

• Omitting parentheses
• Using wrong keywords
• Using brackets instead of parentheses

3. What is the output of the following code?

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

console.log(add(3, 4));

medium

A. 7

B. 34

C. undefined

D. NaN

Solution

1. Step 1: Understand function parameters and return

   The function add takes two numbers and returns their sum.

2. Step 2: Calculate the return value for add(3, 4)

   3 + 4 equals 7, so the function returns 7.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Return adds numbers, not concatenates without strings [OK]

Common Mistakes:

• Treating numbers as strings
• Missing return statement
• Confusing output with parameters

4. Find the error in this code snippet:

function sayHi() {
  console.log('Hi!');
}
sayHi

medium

A. Missing parentheses to call the function.

B. Function name is incorrect.

C. console.log syntax error.

D. Function cannot be called outside definition.

Solution

1. Step 1: Check how the function is called

   The function sayHi is referenced but not called because parentheses are missing.

2. Step 2: Understand function call syntax

   To run the function, it must be called with parentheses: sayHi();

3. Final Answer:

   Missing parentheses to call the function. -> Option A

4. Quick Check:

   Function call needs () [OK]

Hint: Always use () to call functions [OK]

Common Mistakes:

• Forgetting parentheses
• Confusing function reference with call
• Assuming function runs automatically

5. Consider this code:

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

function calculate() {
  let result = multiply(2, 3);
  return result + 4;
}

console.log(calculate());

What is the output and why?

hard

A. 7, because multiply returns 3 and 3 + 4 = 7.

B. 24, because multiply returns 6 and 6 * 4 = 24.

C. 10, because multiply returns 6 and 6 + 4 = 10.

D. Error, because multiply is not called inside calculate.

Solution

1. Step 1: Trace multiply function call

   Calling multiply(2, 3) returns 2 * 3 = 6.

2. Step 2: Calculate final result in calculate

   The variable result is 6, then result + 4 equals 10.

3. Final Answer:

   10, because multiply returns 6 and 6 + 4 = 10. -> Option C

4. Quick Check:

   2*3=6; 6+4=10 [OK]

Hint: Follow return values step-by-step [OK]

Common Mistakes:

• Multiplying instead of adding final step
• Ignoring return values
• Assuming function not called