How can I define these two variables?

Does anyone know how I can define the firstNumber and secondNumber variables in the operator function? I know variables in functions won't register in other functions, but I need to find out if there is another way.

// making a function to store the code block in

var name = prompt("What is your name?"); console.log(name);

window.onload = function calculator() { // creating prompts for the user to type their answers // creating alerts to increase interactivity

alert(name + ", my name is Mr. Calculator, I can help you out with your math problems!");

var firstNumber = prompt(name + ", what is your first number?"); console.log(firstNumber); firstNumber += parseInt(firstNumber); if (!isNaN(firstNumber)) { numbers(); } else { alert("That is not an acceptable value, restart the program to try again"); } }; // creating a conditional function

function numbers() { var secondNumber = prompt("What is your second number, " + name); console.log(secondNumber); secondNumber += parseInt(secondNumber); if(!isNaN(secondNumber)) { operator(); } else { alert("That is not an acceptable value, restart the program to try again"); } }

// creating another conditional function

function operator() { var operation = prompt(name + ", what would you like to do to your two numbers?"); console.log(operation); if (operation === "+") { alert(name + " , the answer is " + firstNumber + secondNumber); } else if (operation === "-") { alert(name + " , the answer is " + firstNumber - secondNumber); } else if (operation === "*") { alert(name + " , the answer is " + firstNumber * secondNumber); } else if (operation === "/") { alert(name + " , the answer is " + firstNumber / secondNumber); } else { alert("That is not an acceptable operator, restart the program to try again"); } }