# About this series

This is series of daily JavaScript coding challenges... for both beginners and advanced users.

Each day I’m gone present you a very simple coding challenge, together with the solution. The solution is intentionally written in a didactic way using classic JavaScript syntax in order to be accessible to coders of all levels.

Solutions are designed with increase level of complexity.

## Today’s coding challenge

```
Implement the Caesar cypher
```

(scroll down for solution)

## Code newbies

If you are a code newbie, try to work on the solution on your own. After you finish it, or if you need help, please consult the provided solution.

## Advanced developers

Please provide alternative solutions in the comments below.

You can solve it using functional concepts or solve it using a different algorithm... or just solve it using the latest ES innovations.

By providing a new solution you can show code newbies different ways to solve the same problem.

## Solution

```
// Solution for challenge39
var text = "I LOVE JAVASCRIPT";
var textEnc = encrypt(text, 13);
var textDec = decrypt(textEnc, 13);
println(text);
println(textEnc);
println(textDec);
// Decrypt a message by using the same encrypt function
// ... but using the inverse of the key (e.g. rotate in the other direction)
function decrypt(msg, key)
{
return encrypt(msg, key * -1);
}
// Function will implement Caesar Cipher to
// encrypt / decrypt the msg by shifting the letters
// of the message acording to the key
function encrypt(msg, key)
{
var encMsg = "";
for(var i = 0; i < msg.length; i++)
{
var code = msg.charCodeAt(i);
// Encrypt only letters in 'A' ... 'Z' interval
if (code >= 65 && code <= 65 + 26 - 1)
{
code -= 65;
code = mod(code + key, 26);
code += 65;
}
encMsg += String.fromCharCode(code);
}
return encMsg;
}
// Modulo function: n mod p
function mod(n, p)
{
if ( n < 0 )
n = p - Math.abs(n) % p;
return n % p;
}
```

To quickly verify this solution, copy the code above in this coding editor and press "Run".

Note: The solution was originally designed for codeguppy.com environment, and therefore is making use of

`println`

. This is the almost equivalent of`console.log`

in other environments. Please feel free to use your preferred coding playground / environment when implementing your solution.

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