Simple Calculator

This project was bootstrapped with Create React App.

Features

• Perform simple calculations (add, subtract, multiply, divide) on numbers (integers and floats, both negative and non-negative allowed). This is feasible via the mathjs library.
• Check validity of input expressions before feeding them into mathjs.
• Update calculated results in real-time across all open browser tabs or windows.
• Persist result entries over time, although only displaying the last 10 entries.

Usage

The app requires two environment variables: DATABASE_URL and TABLE_NAME which indicate where to fetch and save your evaluated math expressions. From the project's root directory, cp .env.sample .env then replace the correct credentials to the placeholders.

Run

Assuming you have already followed the notes under Usage.

• Development mode: (the app will auto-open a browser window or tab at http://localhost:3000)

yarn
yarn dev

• Production mode: (you will have to manually open http://localhost:5000 in your browser once the app starts)

yarn
yarn build
NODE_ENV=production yarn start # note to self: replacing `yarn start` with `heroku local` does the same thing

Development

• To test out the real-time broadcast feature locally:
  • yarn dev in one terminal. This will fire up the server (on port 5000) and one client session (on Create React App default port: 3000)
  • PORT=3001 yarn client in another terminal. This will open a second client session, running on port 3001. (Of course, you can specify any other port as wished.) Note that this is the command for Linux (and probably macOS as well). For Windows, you'll probably want set PORT=3001 && yarn client.