Reverse Polish notation

random.js

var input = `15 7 1 1 + − ÷ 3 × 2 1 1 + + −`
var processed_input = input.split(' ')

function RPN() {
    var stack = [];
    var f = function() {
    };
    f.size = function() {
        return stack.length;
    }
    f.exe = function(v) {
        if (v === '+') {
            var res = stack.pop() + stack.pop();
            stack.push(res);
            return;
        }
        if (v === '*') {
            var res = stack.pop() * stack.pop();
            stack.push(res);
            return;
        }
        if (v === '-') {
            var res = stack.pop() - stack.pop();
            stack.push(res);
            return;
        }
        if (v === '/') {
            var res = stack.pop() / stack.pop();
            stack.push(res);
            return;
        }
        if (v === '=') {
            return stack.pop();
        }
        stack.push(v);
    };
    return f;
}

var input = `15 7 1 1 + - / 3 * 2 1 1 + + -`

function MathSolver() {

    this.solvePostfix = function(postfix) {
        var resultStack = [];
        postfix = postfix.split(" ");
        for(var i = 0; i < postfix.length; i++) {
            if(postfix[i].isNumeric()) {
                resultStack.push(postfix[i]);
            } else {
                var a = resultStack.pop();
                var b = resultStack.pop();
                if(postfix[i] === "+") {
                    resultStack.push(`${parseInt(a) + parseInt(b)}`);
                } else if(postfix[i] === "-") {
                    resultStack.push(`${parseInt(b) - parseInt(a)}`);
                } else if(postfix[i] === "*") {
                    resultStack.push(`${parseInt(a) * parseInt(b)}`);
                } else if(postfix[i] === "/") {
                    resultStack.push(`${parseInt(b) / parseInt(a)}`);
                } else if(postfix[i] === "^") {
                    resultStack.push(`${Math.pow(parseInt(b), parseInt(a))}`);
                }
            }
        }
        if(resultStack.length > 1) {
            return "error";
        } else {
            return resultStack.pop();
        }
    }

}

// =======================================================

String.prototype.isNumeric = function() {
    return !isNaN(parseFloat(this)) && isFinite(this);
}

this.solvePostfix = function(postfix) {
        var resultStack = [];
        postfix = postfix.split(" ");
        for(var i = 0; i < postfix.length; i++) {
            if(postfix[i].isNumeric()) {
                resultStack.push(postfix[i]);
            } else {
                var a = resultStack.pop();
                var b = resultStack.pop();
                if(postfix[i] === "+") {
                    resultStack.push(parseInt(a) + parseInt(b));
                } else if(postfix[i] === "-") {
                    resultStack.push(parseInt(b) - parseInt(a));
                } else if(postfix[i] === "*") {
                    resultStack.push(parseInt(a) * parseInt(b));
                } else if(postfix[i] === "/") {
                    resultStack.push(parseInt(b) / parseInt(a));
                } else if(postfix[i] === "^") {
                    resultStack.push(Math.pow(parseInt(b), parseInt(a)));
                }
            }
        }
        if(resultStack.length > 1) {
            return "error";
        } else {
            // return resultStack.pop();
            return  resultStack;
        }
    }