calculator.js

calculator.js

var calculate = function (s) {
    const stackData = lexer(s);
    // console.log({stackData});
    return run(stackData);
};

function run(stack) {
    let pos = 0;

    function match(c) {
        // console.log(match.caller, match.arguments);
        if (stack[pos] === c) {
            pos++;
            return true;
        }
        return false;
    }

    function factor() {
        const oper = match('-') ? -1 : 1;
        let num;
        if (match('(')) {
            num = exp();
            match(')');
        } else {
            num = stack[pos++];
        }
        return oper + num;
    }

    function term() {
        let num = factor();
        while (true) {
            if (match('x')) {
                num *= factor();
            } else if (match('÷')) {
                num = (num / factor()) >> 0;
            } else {
                return num;
            }
        }
    }

    function exp() {
        let num = term();
        while (true) {
            if (match('+')) {
                num += term();
            } else if (match('-')) {
                num -= term();
            } else {
                return num;
            }
        }
    }

    return exp();
}

function lexer(s) {
    const stack = [];
    let i = 0;
    while (i < s.length) {
        const c = s[i];
        if (c === '+' || c === '-' || c === 'x' || c === '÷' || c === '(' || c === ')') {
            stack.push(c);
            i++;
        } else if (c >= '0' && c <= '9') {
            let num = Number(s[i++]);
            while (s[i] >= '0' && s[i] <= '9') {
                num = num * 10 + Number(s[i++]);
            }
            stack.push(num);
        } else {
            i++;
        }
    }
    return stack;
}

function infixToPostfix(expression) {
    if (typeof expression !== 'string') {
      if (expression instanceof String) {
        expression = expression.toString();
      } else {
        return null;
      }
    }

    var result = '';
    var stack = [];
    var operators = ['*','/','+','-'];
    var tokens = expression.match(/(-?(?:\d+\.?\d*|-?\.\d*))|[()+\-*/]/gi);
    var containsInvalidChars = /[^()+\-*/0-9.\s]/gi.test(expression);

    console.log(tokens, 'is token');
    if (Array.isArray(tokens) && !containsInvalidChars) {
      for (var i = 0; i < tokens.length; i++) {
        var token = tokens[i];

        if (operators.indexOf(token) > -1) {
          while (stack.length && operators.indexOf(stack[stack.length-1]) > -1) {
            var operator = stack.pop();
            result += (' ' + operator);
          }

          stack.push(token);
        } else if (token === '(') {
          stack.push(token);
        } else if (token === ')') {
          var item = stack.pop();

          while (item !== '(') {
            result += (' ' + item);
            item = stack.pop();
          }
        } else if (token) {
          result += (' ' + token);
        }
      }
    }

    while (stack.length) {
      var item = stack.pop();
      result += (' ' + item);
    }

    result = result.trim();

    return (result.length >= 1 ? result : null);
  }

let s = "((15 ÷ (7 - (1 + 1) ) ) x -3) - (2 + (1 + 1))";
// let s = '((3 * 4) / (2 + 5)) * (3 + 4)';
// let s = '((15 / (7 - (1 + 1) ) ) * -3) - (2 + (1 + 1))';
s = s.replaceAll(' ', ''); // trim
const ans = calculate(s);
// console.log({ ans });


const res = infixToPostfix(s);
console.log(res)