Calculator

A calculator (console application) built with Node.js

Description

This application allows the user to input verbal math expressions and gets the results using Syntax Tree.

Available operators:

• plus
• minus
• times
• divided

Samples:

Input	Result
1 plus 3 minus 4	0
1 plus (3 times 4)	13
1 plus 1	2
1000 minus 1	999
2 plus 1 minus 5 divided 2 minus 1	-0.5
4 times 4	16
20 divided 5	4
0.5 times 10	5

Please, check the Implementation section for more details.

Main technologies used

• Node.js: JavaScript runtime built on Chrome's V8 engine
• TypeScript: Typed JavaScript at Any Scale
• Jest for unit tests
• ESLint and Prettier to enforce code styling
• Husky to force syntax checking before commits

Requirements

For local usage:

• Node.js (v14+)
• npm

For local usage with Docker:

• Docker Engine

Running

With Docker

• Be sure you have Docker installed.
• Build image and run the container:

docker build -t calculator .
docker run -it calculator:latest /bin/sh

• Start the application:

node dist/app.js

Without Docker

Be sure to install the requirements. If using nvm, you can easily run:

nvm use

• Install dependencies and start the application:

  npm install
  
  # development
  npm run start:dev
  
  # production
  npm run build
  npm run start

Running unit tests

   npm run test:cover

   npm run test

Implementation

This application uses stdin and stdout as an entry point for the system (just because this way is more simple than implementing a REST API).

How does it work?

Let's considerate this expression:

2 plus 5 times 3

1. Given the expression;
2. Uses Regular Expression just to early avoid typos;
3. Convert the original expression into a list of tokens:
4. Parse the tokens, respecting the order of the operators (saliency), to calculate the final result.

• It's required to follow the math concept of BODMAS. Here is an article about BODMAS. In resume:
  • Do things in Parentheses First
  • Multiply or Divide before you Add or Subtract
  • Otherwise just go left to right