A function to replace characters

package.json

{
  "name": "replace-character",
  "version": "1.0.0",
  "author": "coolreader18",
  "main": "Replace-character.js",
  "repo": "gist:9d372c8604fb918a19e7d9647c863cb1",
  "license": "MIT"
}

Replace-character.js

/* @legume
 * @name replace-character
 * @version 1.0.0
 */
(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
    define('replace-character', [], factory);
  } else if (typeof module === 'object' && module.exports) {
    module.exports = factory();
  } else {
    root.replaceCharacter = factory();
  }
}(typeof self !== 'undefined' ? self : this, function () {

  /**
   * Replaces specified characters with others.
   * @param {string} input - The input string.
   * @param {Object} replacements - The keys are the letter to replace and the values are the letters getting replaced.
   * @param {boolean} [filter=false] - Whether or not to filter out all characters that aren't one of replacements's keys.
   */
  return function replaceCharacter(input, replacements, filter = false) {
    var ret = Array.from(input);
    var counts = Object.keys(replacements)
      .reduce((obj, cur) => (obj[cur] = -1, obj), {});
    if (filter)
      ret = ret.filter(cur => Object.keys(replacements).includes(cur));
    return ret.map((cur, i) => {
      var replace = replacements[cur];
      counts[cur]++;
      return ({
      	string: () => replace,
      	"function": () => replace(counts[cur], i),
        undefined: () => cur
      })[typeof replace]();
    }).join("");
  };

}));