Addition is not working in JavaScript

I am trying to learn Javascript. Here I am confused with the following code.

http://rendera.heroku.com/usercode/eae2b0f40cf503b36ee346f5c511b0e29fc82f9e

When I put x+y in the function it is going wrong. For example 2+2=22, 5+7=57

But /, *, - are working. Why is + not working? Please help me. Thanks a lot in advance

One or both of the variables is a string instead of a number. This makes the + do string concatenation.

'2' + 2 === '22';  // true

2 + 2 === 4;  // true

The other arithmetic operators / * - will perform a toNumber conversion on the string(s).

'3' * '5' === 15;  // true

A quick way to convert a string to a number is to use the unary + operator.

+'2' + 2 === 4;  // true

...or with your variables:

+x + +y

+ has two uses. One is addition, the other however is string concatenation. If one or both of your variables is a string, then + will concatenate them.

You will need to use parseInt or parseFloat to turn a string into a number.

In Javascript the + operator can either perform addition or concatenation depending on the type of its operands. When numbers are used with + it uses addition, but when strings are used with + it concatenates (joins the strings) instead