Return values in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the return statement do in a JavaScript function?

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

beginner

Can a JavaScript function return more than one value directly?

No, a function returns only one value. But you can return an object or array to hold multiple values.

beginner

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

The function returns undefined by default.

beginner

How do you capture the value returned by a function?

You assign the function call to a variable, like <code>let result = myFunction();</code>

beginner

What is the difference between console.log() and return in a function?

console.log() shows output on the screen but does not send a value back. return sends a value back to the caller.

What does a return statement do inside a function?

A Stops the function and sends a value back

B Prints a value to the console

C Starts the function

D Declares a variable

The return statement stops the function and sends a value back to where it was called.

What value does a function return if it has no return statement?

A null

B 0

C undefined

D false

Functions without a return statement return undefined by default.

How can you return multiple values from a function?

A You cannot return multiple values

B Use multiple <code>return</code> statements

C Return a string with all values

D Return an array or object containing the values

You can return an array or object to hold multiple values from a function.

Which of these captures the returned value from a function?

A let x = myFunction()

B console.log(myFunction())

C return myFunction()

D function myFunction()

Assigning the function call to a variable captures the returned value.

What is the difference between return and console.log()?

A <code>return</code> prints output, <code>console.log()</code> sends value back

B <code>return</code> sends value back, <code>console.log()</code> prints output

C Both do the same thing

D Neither sends value back

return sends a value back to the caller; console.log() only prints to the console.

Explain what the return statement does in a JavaScript function and why it is useful.

Think about how functions give you answers.

Describe how you can return multiple values from a function in JavaScript.

Imagine putting things in a box to carry them all at once.

Practice

1. What does the return statement do in a JavaScript function?

easy

A. It pauses the function but continues later.

B. It prints a value to the screen.

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

D. It creates a new variable inside the function.

Solution

1. Step 1: Understand the purpose of return

   The return statement sends a value back to the place where the function was called.

2. Step 2: Recognize function behavior after return

   After return, the function stops running and no further code inside it executes.

3. Final Answer:

   It sends a value back to where the function was called. -> Option C

4. Quick Check:

   Return sends value back [OK]

Hint: Return sends value back and stops function [OK]

Common Mistakes:

• Thinking return prints output
• Believing return pauses function
• Confusing return with variable creation

2. Which of the following is the correct syntax to return the value 10 from a function?

easy

A. return 10;

B. return = 10;

C. return: 10;

D. return => 10;

Solution

1. Step 1: Identify correct return syntax

   The correct syntax to return a value is return value; with a semicolon.

2. Step 2: Check each option

   return 10; uses return 10; which is correct. return = 10; uses equals sign for assignment, invalid. return: 10; uses colon which is invalid. return => 10; uses arrow syntax incorrectly.

3. Final Answer:

   return 10; -> Option A

4. Quick Check:

   Correct return syntax ends with semicolon [OK]

Hint: Use 'return value;' with semicolon [OK]

Common Mistakes:

• Using colon instead of semicolon
• Confusing arrow functions with return syntax
• Using = for assignment with return

3. What is the output of this 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 behavior

   The function add takes two numbers and returns their sum using return a + b;.

2. Step 2: Calculate the return value

   Calling add(3, 4) returns 3 + 4 = 7, which is printed by console.log.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   Sum of 3 and 4 is 7 [OK]

Hint: Return adds numbers and prints result [OK]

Common Mistakes:

• Concatenating numbers as strings
• Forgetting to return value
• Expecting undefined without return

4. Find the error in this function:

function greet(name) {
  console.log('Hello ' + name);
  return;
  console.log('Goodbye');
}

medium

A. The function syntax is invalid.

B. Missing return value causes error.

C. The function should not use console.log.

D. The function returns before printing 'Goodbye', so 'Goodbye' never shows.

Solution

1. Step 1: Analyze function flow

   The function prints 'Hello ' plus the name, then hits return; which stops the function.

2. Step 2: Check code after return

   Code after return (printing 'Goodbye') never runs, so 'Goodbye' is never printed.

3. Final Answer:

   The function returns before printing 'Goodbye', so 'Goodbye' never shows. -> Option D

4. Quick Check:

   Code after return is skipped [OK]

Hint: Code after return does not run [OK]

Common Mistakes:

• Expecting code after return to run
• Thinking missing return value causes error
• Confusing console.log with return

5. You want a function that returns the first non-empty string from an array or returns 'No valid string' if none found. Which function correctly uses return values?

hard

A. function firstNonEmpty(arr) {
arr.forEach(str => {
if (str) return str;
});
return 'No valid string';
}

B. function firstNonEmpty(arr) {
for (const str of arr) {
if (str) return str;
}
return 'No valid string';
}

C. function firstNonEmpty(arr) {
let result = '';
arr.forEach(str => {
if (str) result = str;
});
return result || 'No valid string';
}

D. function firstNonEmpty(arr) {
for (let i = 0; i < arr.length; i++) {
if (arr[i] === '') return arr[i];
}
return 'No valid string';
}

Solution

1. Step 1: Understand the goal

   The function must return the first non-empty string or a default message if none found.

2. Step 2: Evaluate each function

   function firstNonEmpty(arr) { for (const str of arr) { if (str) return str; } return 'No valid string'; } uses a for-of loop and returns immediately when a non-empty string is found, else returns default. This is correct.
   function firstNonEmpty(arr) { arr.forEach(str => { if (str) return str; }); return 'No valid string'; } uses forEach with return inside callback, which does not stop the outer function.
   function firstNonEmpty(arr) { let result = ''; arr.forEach(str => { if (str) result = str; }); return result || 'No valid string'; } collects last non-empty string but does not return first.
   function firstNonEmpty(arr) { for (let i = 0; i < arr.length; i++) { if (arr[i] === '') return arr[i]; } return 'No valid string'; } returns empty string if found, which is opposite of requirement.

3. Final Answer:

   function firstNonEmpty(arr) { for (const str of arr) { if (str) return str; } return 'No valid string'; } -> Option B

4. Quick Check:

   Return inside loop stops function immediately [OK]

Hint: Use return inside loop to exit early [OK]

Common Mistakes:

• Using forEach with return expecting to exit function
• Returning empty string instead of non-empty
• Returning last instead of first non-empty string