Node.JS stack calculator

_NodeJS_stack_caculator.md

Stack I used https://github.com/bishil06/data_structure/blob/main/src/stack/Stack.js

1. convert infix notation to postfix notation
2. operator push stack
3. calculate

stackCalculator.js

const Stack = require('./Stack.js');

const operators = {
    '(': 0,
    ')': 0,
    '+': 1,
    '-': 1,
    '*': 2,
    '/': 2,
}
const op = new Map(Object.entries(operators));

function *filter(fn, iter) {
    for(const v of iter) if (fn(v)) yield v;
}

function *convToPRNExp(expression) {
    const stack = new Stack();
    let numStr = '';

    for(const c of filter(c => (c !== ' '), expression)) {
        if (op.has(c)) {
            // operator process
            if (numStr !== '') yield Number(numStr);
            numStr = '';

            if (!stack.isEmpty() && op.get(stack.peek()) > op.get(c)) {
                yield* filter(op => (op !=='(' && op !== ')'), stack);
                stack.push(c);
            }
            else {
                stack.push(c);
            }
        }
        else {
            // number process
            numStr += c;
        }
    }
    if (numStr !== '') yield Number(numStr);

    yield* filter(op => (op !=='(' && op !== ')'), stack);
}

function stackCalculator(expression) {
    let stack = new Stack();

    for(const e of convToPRNExp(expression)) {
        if (op.has(e)) {
            let a = stack.pop();
            let b = stack.pop();
            switch(e) {
                case '+':
                    stack.push(b+a);
                    break;
                case '-':
                    stack.push(b-a);
                    break;
                case '*':
                    stack.push(b*a);
                    break;
                case '/':
                    stack.push(b/a);
                    break;
            }
        }
        else {
            stack.push(e)
        }
    }

    return stack.pop();
}

console.log(stackCalculator('1+2')); // 3
console.log(stackCalculator('(1+2)*2')); // 6
console.log(stackCalculator('(1+2*3)+2')); // 9
console.log(stackCalculator('(1+2*50)+10')); // 111