Unary operators in Javascript - Mini Project: Build & Apply

Unary Operators in JavaScript

📖 Scenario: You are working on a simple calculator app that needs to handle increasing and decreasing numbers by one. This is common in counters, like counting items in a shopping cart or tracking steps in a game.

🎯 Goal: Build a small program that uses unary operators to increase and decrease a number by one.

📋 What You'll Learn

Create a variable with an initial number

Create a variable to hold the incremented number using the increment operator ++

Create a variable to hold the decremented number using the decrement operator --

Print the original, incremented, and decremented numbers

💡 Why This Matters

🌍 Real World

Counters are everywhere: counting clicks, items in a cart, or steps in a game. Unary operators make these tasks simple and fast.

💼 Career

Understanding unary operators is essential for writing clean and efficient code in many programming jobs, especially in frontend and backend development.

1

Create the initial number variable

Create a variable called count and set it to the number 10.

Javascript

# Your code here

Hint

Use let to create a variable named count and assign it the value 10.

2

Create incremented number using increment operator

Create a variable called incremented and set it to count plus one using the increment operator ++.

Javascript

let count = 10;
# Your code here

Hint

Use the prefix increment operator ++count to add one to count and assign it to incremented.

3

Create decremented number using decrement operator

Create a variable called decremented and set it to incremented minus one using the decrement operator --.

Javascript

let count = 10;
let incremented = ++count;
# Your code here

Hint

Use the prefix decrement operator --incremented to subtract one from incremented and assign it to decremented.

4

Print all three numbers

Use console.log to print the values of count, incremented, and decremented each on a new line.

Javascript

let count = 10;
let incremented = ++count;
let decremented = --incremented;
# Your code here

Hint

Use three console.log statements to print each variable on its own line.

Practice

1. Which of the following is a unary operator in JavaScript?

easy

A. ++

B. +=

C. &&

D. ===

Solution

1. Step 1: Understand unary operator definition

   A unary operator works with only one operand (value).

2. Step 2: Identify unary operators in options

   ++ increments a single variable by 1, so it is unary. += and && require two operands, === compares two values.

3. Final Answer:

   ++ -> Option A

4. Quick Check:

   Unary operator = ++ [OK]

Hint: Unary operators work on one value only, like ++ or -- [OK]

Common Mistakes:

• Confusing += as unary instead of binary
• Thinking && is unary when it's binary
• Mixing comparison operators with unary

2. Which of the following is the correct syntax to decrement variable x by 1 using a unary operator?

easy

A. --x-

B. x--

C. x-=

D. x--x

Solution

1. Step 1: Recall decrement unary operator syntax

   The decrement operator is written as -- before or after the variable.

2. Step 2: Check each option for correct syntax

   x-- is valid and decreases x by 1. x-= is incomplete syntax. --x- and x--x are invalid.

3. Final Answer:

   x-- -> Option B

4. Quick Check:

   Decrement syntax = x-- [OK]

Hint: Decrement uses -- placed before or after variable [OK]

Common Mistakes:

• Using x-= instead of x--
• Adding extra characters like x--x
• Placing -- incorrectly like --x-

3. What is the output of the following code?

let a = 5;
console.log(-a);

medium

A. -5

B. 5

C. NaN

D. undefined

Solution

1. Step 1: Understand unary minus operator

   The unary minus operator (-) changes the sign of the number.

2. Step 2: Apply unary minus to variable a

   a is 5, so -a becomes -5.

3. Final Answer:

   -5 -> Option A

4. Quick Check:

   Unary minus of 5 = -5 [OK]

Hint: Unary minus flips sign: positive to negative [OK]

Common Mistakes:

• Confusing unary minus with subtraction
• Expecting output 5 instead of -5
• Thinking it returns NaN or undefined

4. Find the error in this code snippet:

let count = 10;
count = ++;

medium

A. Syntax error due to missing semicolon

B. Incorrect use of decrement operator

C. Missing variable after ++ operator

D. No error, code runs fine

Solution

1. Step 1: Analyze the use of ++ operator

   The ++ operator must be used with a variable, either before or after it.

2. Step 2: Identify the error in the code

   Here, ++ is used alone without a variable, causing a syntax error.

3. Final Answer:

   Missing variable after ++ operator -> Option C

4. Quick Check:

   ++ needs a variable to work [OK]

Hint: ++ must be attached to a variable, not alone [OK]

Common Mistakes:

• Thinking ++ alone increments something
• Ignoring syntax errors from incomplete expressions
• Confusing missing semicolon as main error

5. Given the code below, what will be the value of result?

let x = 3;
let y = ++x + x++ + --x;
let result = y;

hard

A. 10

B. 13

C. 11

D. 12

Solution

1. Step 1: Evaluate ++x (pre-increment)

   ++x increases x from 3 to 4, returns 4.

2. Step 2: Evaluate x++ (post-increment)

   x++ returns current x (4), then increments x to 5.

3. Step 3: Evaluate --x (pre-decrement)

   --x decreases x from 5 to 4, returns 4.

4. Step 4: Calculate y

   y = 4 + 4 + 4 = 12.

5. Step 5: Check final value of result

   result = y = 12.

6. Final Answer:

   12 -> Option D

7. Quick Check:

   Pre/post increments affect value and order [OK]

Hint: Pre-increment changes value before use; post-increment after [OK]

Common Mistakes:

• Ignoring order of increments and decrements
• Mixing pre- and post-increment results
• Calculating without updating variable values