JavaScript Practice 13/21

Caesar cipher

Every character has a numeric code - "a".charCodeAt(0) is 97, "z" is 122. Subtract the code of "a" (or "A" for uppercase) from a letter's code and you get its position in the alphabet, 0 through 25. Shift that position, wrap it with % 26 so it stays in range, and add the base code back to get the new letter.

str.replace(/[a-zA-Z]/g, fn) is the piece that ties it together: the g flag runs fn on every letter in the string, one at a time, and anything that isn't a letter - spaces, punctuation, digits - passes through untouched because the pattern never matches it.

Your task: write encode(str, shift), shifting every letter in str forward by shift places in the alphabet, wrapping from z back to a (and Z to A), preserving each letter's case, and leaving non-letters exactly as they are.

You'll practice:

Converting between a character and its alphabet position with char codes
Replacing every match in a string with .replace(/.../g, fn)

// Write encode(str, shift): shift every LETTER in str forward by shift
// places in the alphabet, wrapping around from z to a. Preserve case,
// and leave anything that is not a letter (spaces, punctuation) untouched.
function encode(str, shift) {

}