NodeJS: How to create a shorthash, but NOT smart way!

example-create-shorthash.js

/**
 * Create a short hash to **roughly** specify the accessed user's identity.
 * The generated hash could be immutable only when either user's IP address and access date are same.
 *
 * CAUTION: 
 * NEVER use it for generate unique ID, it could NOT be unique!
 */
const crypto = require("crypto");

var text = "2018/04/01 xxx.xxx.xxx.xxx"; // "<Date> <IP>"
console.log(shorthash(text)); // "TVBXCl"

var text = "2018/04/01 yyy.yyy.yyy.yyy"; // "<Date> <IP>"
console.log(shorthash(text)); // "vG0Nto"

function shorthash(s, len = 6) {
  const b64 = crypto.createHash("md5").update(s, "binary").digest("base64");
  return b64.substring(0, len);
}