JavaScript Program to Create Simple Calculator

You can create a simple calculator in JavaScript by defining a function like function calculator(num1, num2, operator) { if (operator === '+') return num1 + num2; else if (operator === '-') return num1 - num2; else if (operator === '*') return num1 * num2; else if (operator === '/') return num1 / num2; else return 'Invalid operator'; } which takes two numbers and an operator to return the calculation result.

Examples

Inputcalculator(5, 3, '+')

Output8

Inputcalculator(10, 2, '*')

Output20

Inputcalculator(7, 0, '/')

OutputInfinity

How to Think About It

To build a simple calculator, think of it as a tool that takes two numbers and an operation symbol like +, -, *, or /. You check which operation the user wants, then perform that operation on the two numbers and give back the answer.

Algorithm

1

Get the first number input.

2

Get the second number input.

3

Get the operator input (+, -, *, /).

4

Check which operator was given.

5

Perform the corresponding arithmetic operation.

6

Return or display the result.

Code

javascript

function calculator(num1, num2, operator) {
  if (operator === '+') return num1 + num2;
  else if (operator === '-') return num1 - num2;
  else if (operator === '*') return num1 * num2;
  else if (operator === '/') return num1 / num2;
  else return 'Invalid operator';
}

console.log(calculator(5, 3, '+')); // 8
console.log(calculator(10, 2, '*')); // 20
console.log(calculator(7, 0, '/')); // Infinity

Output

8
20
Infinity

Dry Run

Let's trace calculator(5, 3, '+') through the code

1

Receive inputs

num1 = 5, num2 = 3, operator = '+'

2

Check operator

operator is '+' so perform addition

3

Calculate result

5 + 3 = 8

4

Return result

Return 8

Step	Operation	Result
1	Inputs received	num1=5, num2=3, operator='+'
2	Check operator	operator is '+'
3	Perform addition	5 + 3 = 8
4	Return result	8

Why This Works

Step 1: Input handling

The function takes two numbers and an operator as inputs to know what to calculate.

Step 2: Operator check

It uses if and else if to find which arithmetic operation to perform.

Step 3: Perform calculation

Based on the operator, it does addition, subtraction, multiplication, or division using +, -, *, or /.

Step 4: Return result

The function returns the calculated value or an error message if the operator is invalid.

Alternative Approaches

Using switch statement

javascript

function calculator(num1, num2, operator) {
  switch(operator) {
    case '+': return num1 + num2;
    case '-': return num1 - num2;
    case '*': return num1 * num2;
    case '/': return num1 / num2;
    default: return 'Invalid operator';
  }
}

console.log(calculator(4, 2, '-')); // 2

Switch makes the code cleaner and easier to read when checking multiple cases.

Using an object map for operations

javascript

const operations = {
  '+': (a, b) => a + b,
  '-': (a, b) => a - b,
  '*': (a, b) => a * b,
  '/': (a, b) => a / b
};

function calculator(num1, num2, operator) {
  const operation = operations[operator];
  return operation ? operation(num1, num2) : 'Invalid operator';
}

console.log(calculator(6, 3, '/')); // 2

Using an object map allows easy extension and cleaner code without many if/else or switch.

Complexity: O(1) time, O(1) space

Time Complexity

The calculator performs a fixed number of checks and one arithmetic operation, so it runs in constant time.

Space Complexity

It uses a fixed amount of memory for inputs and no extra data structures, so space is constant.

Which Approach is Fastest?

All approaches run in constant time; using an object map is clean and scalable, while if/else or switch are straightforward.

Approach	Time	Space	Best For
If/Else	O(1)	O(1)	Simple and direct checks
Switch Statement	O(1)	O(1)	Cleaner multiple case handling
Object Map	O(1)	O(1)	Easy to extend and maintain