index.js

/**
 * Expose `rndid`.
 */

exports = module.exports = rndid;

/**
 * Default ID length.
 */

exports.defaultLength = 7;

/**
 * Return a guaranteed unique id of the provided
 * `length`, optionally prefixed with `prefix`.
 *
 * If no length is provided, will use
 * `rndid.defaultLength`.
 *
 * @api private
 * @param {String} [prefix]
 * @param {Number} [length]
 * @return {String}
 */

function rndid(prefix, length) {
  if ('number' == typeof prefix)
    length = prefix, prefix = '';
  length = length || exports.defaultLength;
  var id = (prefix || '') + str(length);
  if (document.getElementById(id)) return rndid(prefix, length);
  return id;
}

/**
 * Generate a random alpha-char.
 *
 * @api private
 * @return {String}
 */

function character() {
  return String.fromCharCode(Math.floor(Math.random() * 25) + 97);
}

/**
 * Generate a random alpha-string of `len` characters.
 *
 * @api private
 * @param {Number} len
 * @return {String}
 */

function str(len) {
  for (var i = 0, s = ''; i < len; i++) s += character();
  return s;
}