Putting together all the code discussed above, the final code for converting the infix expression to postfix looks like the following: 

function convert(expr) {
    var postfix = "";
    var ops = new Stack();
    var operators = {
        "^": {
            priority: 4,
            associativity: "rtl"
        },
        "*": {
            priority: 3,
            associativity: "ltr"
        },
        "/": {
            priority: 3,
            associativity: "ltr"
        },
        "+": {
            priority: 2,
            associativity: "ltr"
        },
        "-": {
            priority: 2,
            associativity: "ltr"
        }
    };


    expr = clean(expr.trim().replace(/s+/g, "").split(/([+-*/^()])/));

    if (!isBalanced(expr) {
        return 'error';
    }    

    expr.forEach(function(exp) {
        if(!isNaN(parseFloat(exp))) {
            postfix += exp + " ";
        }  else if(exp === "(") {
            ops.push(exp);
        } else if(exp === ")") {
            while(ops.peek() !== "(") {
                postfix += ops.pop() + " ";
            }
            ops.pop();
        } else if("*^+-/".indexOf(exp) !== -1) {
            var currOp = exp;
            var prevOp = ops.peek();
            while("*^+-/".indexOf(prevOp) !== -1 && ((operators[currOp].associativity === "ltr" && operators[currOp].priority <= operators[prevOp].priority) || (operators[currOp].associativity === "rtl" && operators[currOp].priority < operators[prevOp].priority)))
            {
                postfix += ops.pop() + " ";
                prevOp = ops.peek();
            }
            ops.push(currOp);
        }
    });
   
    while(ops.size() > 0) {
        postfix += ops.pop() + " ";
    }
    return postfix;
}

This converts the infix operator provided into the postfix notation.