Improved version with support for buffers

[mkg20001]

const assert = require('assert')

function xor (data, key) {
  assert(data.length <= key.length, 'key length not equal/bigger data length')
  let out = Buffer.alloc(data.length)
  for (var i = 0; i < data.length; i++) {
    out[i] = data[i] ^ key[i]
  }
  return out
}

This improved version can encrypt buffers and use more than one-byte as encryption key

Example:

const crypto = require('crypto')
const key = crypto.randomBytes(16)
const msg = Buffer.from('hi')
const encrypted = xor(msg, key)
const decrypted = xor(encrypted, key)
console.log(String(decrypted))

[RobLoach]

This is a great idea! Mind submitting a PR for it?

[RobLoach]

Getting the following in the browser...

Uncaught ReferenceError: Buffer is not defined
    at xorCrypt (xor-crypt.js:50)
    at HTMLButtonElement.<anonymous> ((index):79)
xorCrypt @ xor-crypt.js:50
(anonymous) @ (index):79

Perhaps we could check if Buffer is available, and fallback to strings if not?