Function execution flow in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens first when a JavaScript function is called?

The function's code starts running from the first line inside the function block.

beginner

What is the role of the return statement in a function?

It stops the function and sends a value back to where the function was called.

beginner

What happens if a function does not have a return statement?

The function returns undefined by default after finishing all its code.

intermediate

How does JavaScript handle multiple function calls in a row?

Each function runs completely before the next one starts, following the order they were called.

intermediate

What is the call stack in JavaScript function execution?

It is a structure that keeps track of all the functions that are currently running or waiting to finish.

What does the return statement do inside a function?

A Declares a variable

B Starts the function

C Calls another function

D Stops the function and sends a value back

The return statement stops the function and sends a value back to the caller.

If a function has no return, what is its result when called?

A It returns <code>undefined</code>

B It returns <code>null</code>

C It throws an error

D It returns <code>0</code>

Functions without a return statement return undefined by default.

What order do functions run if called one after another?

A Each runs completely before the next starts

B Last called runs first

C All run at the same time

D They run randomly

Functions run one after another, each finishing before the next starts.

What is the call stack used for in function execution?

A To store variables

B To keep track of running functions

C To manage browser tabs

D To save files

The call stack tracks which functions are running or waiting to finish.

When a function is called, where does execution start?

A At the middle of the function

B At the last line of the function

C At the first line inside the function

D At the return statement

Execution starts at the first line inside the function when it is called.

Explain the flow of execution when a JavaScript function is called.

Think about what happens inside the function and what happens after it finishes.

Describe what the call stack is and how it relates to function execution flow.

Imagine a stack of plates where you add and remove plates in order.

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