Generates a URL safe key with sufficient bit complexity

generate-key.js

/**
 * Generate a URL safe key with sufficient bits of complexity.
 */
const generateKey = function(bits){
  var alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    + "abcdefghijklmnopqrstuvwxyz"
    + "012345678910"
    + "-_"
  var expectedEntroy = Math.pow(2, bits)
  var key = ''
  while(Math.pow(alphabet.length, key.length) < expectedEntroy){
    key += alphabet[Math.floor(Math.random() * alphabet.length)]
  }
  return key
}

// Will result in at least 256 bits of entropy 
console.log(generateKey(256))