Calculator example

calc.js

var number1 = parseFloat(prompt("Enter the first number"));
var number2 = parseFloat(prompt("Enter the second number"));
var operation = prompt("Choose one of +, -, *, /")
var result;

if(operation == "+") {
    result = number1 + number2;
} else if(operation == "-") {
    result = number1 - number2;
} else if(operation == "*") {
    result = number1 * number2;
} else if(operation == "/") {
    result = number1 / number2;
}

alert(result);