Stack: PostFix Calculator

foreach token if token is integer push token else if token is operator pop right side value pop left side value evaluate operator push result next 

function postFixCalc(expression) { //create new stack let stack = new Stack(); //loop through each character in provided expression for (let idx = 0; idx < expression.length; idx++) { //store each character let token = expression[idx]; //if it's a number, push to stack //else pop right side and left side, perform operation and push to stack if (!isNaN(token)) { stack.push(Number(token)); } else { let rhs = stack.pop(); let lhs = stack.pop(); //if right or left side is not available if (rhs === "UnderFlow" || lhs === "UnderFlow" ) { return "Can't perform postfix calculation"; } switch (token) { case '+': stack.push(lhs + rhs); break; case '-': stack.push(lhs - rhs); break; case '*': stack.push(lhs * rhs); break; case '/': stack.push(lhs / rhs); break; case '%': stack.push(lhs % rhs); break; } } }; //return result of calculation return stack.pop(); } 

console.log(postFixCalc('567*+1-'))