This project was bootstrapped with Create React App.

Reverse Polish notation (RPN), also known as Polish postfix notation or simply postfix notation, is a mathematical notation in which operators follow their operands. The calculator can work with a keyboard and the UI to allow you to use single or multiple operators and operands when you input a string. Your operators and operands should be separated by one space.

• the base idea was to use a standard calculator (macOS or Window) with an extra field to see current status of the calculator (stack of operands)
• can work with integer, float and negative numbers
• this calculator allows you to input many operators and operands in one line, they also can be even mixed
• allow using a keyboard or UI buttons
• validate input before computation
• show errors for an input string

• react library to build UI
• RPN Calculator should be an independent service that allows you to use it with different js frameworks or even node.js REPL
• an input string should be validated before computation (made by a regular expression)
• should support extending to add more operators (+, -, *, /, ^, ...)
• to create an operator, you should use a special function (Operator) which provides you to add name, function, regular expression (to understand how to validate it) and count of operands for the function
• react Calculator component as a wrapper to communicate between RPN Calculator service and end-user.

// create the calculator with an empty list of operators
const calculator = new RPNCalculator();

// add operators
calculator.addOperators(
  new Operator('+', (a, b) => a + b),
  new Operator('-', (a, b) => a - b),
  new Operator('*', (a, b) => a * b),
  new Operator('/', (a, b) => a / b),
  new Operator('sqrt', (a) => Math.sqrt(a), 'sqrt', 1),
  new Operator('^', (a, b) => a ** b, '\\^', 2),
);

// use it
calculator.eval('1 2 3 4 + - +');

// to see the result
calculator.numbers(); // [-4]

/**
 * how it works
 * 3 + 4 = 7
 * 2 - 7 = -5
 * 1 + -5 = -4
 */

// if you want to continue
calculator.eval('4'); // [-4, 4]
calculator.eval('+');
calculator.numbers(); // [0]

// if you want to start from scratch
calculator.reset();
calculator.numbers(); // [] - empty stack

// How to use react component
const operators = [new Operator('%', (a, b) => (a / 100) * b, '\\%', 2)];

<Calculator operators={operators} />;

• add unit and integration tests for react Calculator component
• add real-time validation after tapping separator
• add a better way to show errors for end-user
• avoid to input whatever from a keyboard, only numbers, separator (one space) and basic operators (as macOS or Windows calculators do)
• better error handlers for developers

In the project directory, you can run:

Runs the app in the development mode.
Open http://localhost:3000 to view it in the browser.

The page will reload if you make edits.
You will also see any lint errors in the console.

Builds the app for production to the build folder.

To run tests.