Add calculator module with basic arithmetic operations

[Copilot]

Implements a calculator module supporting addition, subtraction, multiplication, and division with proper error handling and validation.

Implementation

• src/calculator.js - Five functions: add(), subtract(), multiply(), divide(), and unified calculate(a, operator, b)
• Input validation - Rejects non-numbers, NaN, Infinity; throws on division by zero
• Error handling - Descriptive error messages for all edge cases

Testing

• 43 tests covering normal operations, edge cases, and error conditions
• 100% coverage across all code paths
• Jest test framework with npm test and npm run test:coverage scripts

Usage

const { add, subtract, multiply, divide, calculate } = require('./src/calculator');

// Individual functions
add(5, 3);           // 8
subtract(10, 4);     // 6
multiply(7, 6);      // 42
divide(20, 4);       // 5

// Unified interface
calculate(5, '+', 3);   // 8
calculate(10, '-', 4);  // 6
calculate(7, '*', 6);   // 42
calculate(20, '/', 4);  // 5

// Error handling
divide(5, 0);        // throws "Division by zero is not allowed"
calculate(5, '%', 3); // throws "Unsupported operator: %"

Demo application in examples/demo.js shows all features. API documentation in CALCULATOR.md.

Original prompt

@develop-agent Task: Create a simple calculator function that supports addition, subtraction, multiplication, and division operations.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.