cannot use + when try to add number

Question

After i selected option 1 and after i add the number like 100 it results like this 100100

This is the code:

var userAmount;
    var userMoney = 100;
         


        

Answer 1

A common mistake for people new to JavaScript is they forget almost every value taken from user input is a String. You'll need to convert these into numbers before you can use the addition + operator. This conversion can be done with the unary + or parseFloat, for example

userAmount = parseFloat(prompt("Amount: "));

When using Strings in JavaScript, the + operator is actually string concatenation