MathSolver.js

function MathSolver() {
 
    this.infixToPostfix = function(infix) {
        var outputQueue = "";
        var operatorStack = [];
        var operators = {
            "^": {
                precedence: 4,
                associativity: "Right"
            },
            "/": {
                precedence: 3,
                associativity: "Left"
            },
            "*": {
                precedence: 3,
                associativity: "Left"
            },
            "+": {
                precedence: 2,
                associativity: "Left"
            },
            "-": {
                precedence: 2,
                associativity: "Left"
            }
        }
        infix = infix.replace(/\s+/g, "");
        infix = infix.split(/([\+\-\*\/\^\(\)])/).clean();
        for(var i = 0; i < infix.length; i++) {
            var token = infix[i];
            if(token.isNumeric()) {
                outputQueue += token + " ";
            } else if("^*/+-".indexOf(token) !== -1) {
                var o1 = token;
                var o2 = operatorStack[operatorStack.length - 1];
                while("^*/+-".indexOf(o2) !== -1 && ((operators[o1].associativity === "Left" && operators[o1].precedence <= operators[o2].precedence) || (operators[o1].associativity === "Right" && operators[o1].precedence < operators[o2].precedence))) {
                    outputQueue += operatorStack.pop() + " ";
                    o2 = operatorStack[operatorStack.length - 1];
                }
                operatorStack.push(o1);
            } else if(token === "(") {
                operatorStack.push(token);
            } else if(token === ")") {
                while(operatorStack[operatorStack.length - 1] !== "(") {
                    outputQueue += operatorStack.pop() + " ";
                }
                operatorStack.pop();
            }
        }
        while(operatorStack.length > 0) {
            outputQueue += operatorStack.pop() + " ";
        }
        return outputQueue;
    }
 
}

MathSolver.test.js

var ms = new MathSolver();
console.log(ms.infixToPostfix("5 + 3 * 6 - ( 5 / 3 ) + 7"));