Base N (N <= 62) encode an integer

base-encode.js

const baseChars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
const base = 62;

function baseEncode(n) {
  let b = base;
  let m = n;
  let ret = '';
  while (b <= n) {
    b = base * (1 + b);
    ret = baseChars[m % base] + ret;
    m = Math.floor(m / base) - 1;
  }
  return baseChars[m % base] + ret;
}