Rail Fence (zigzag) cipher JavaScript implementation

zigzag.js

/**
 * Rail Fence (zigzag) cipher JavaScript implementation.
 * https://en.wikipedia.org/wiki/Rail_fence_cipher
 */
(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
      define([], factory);
  } else if (typeof module === 'object' && module.exports) {
    module.exports = factory();
  } else {
    root.zigzag = factory();
  }
}(this, function () {

  function makeMap( len, n) {
    var i, pip, period = 2 * (n - 1);
    var rows = Array.apply( null, Array( n)).map( function(){ return []}); // array of arrays
    for( i = 0; i < len; i++) {
      pip = i % period;
      r = pip < (n - 1) ? pip : period - pip; 
      rows[ r].push( i);
    }
    return Array.concat.apply(null,rows);
  }
  
  function decrypt( text, n) {
    var i, len = text.length, mapped = makeMap(len,n), result = "";
    return text.split('').reduce(function(p,c,i,a){ return p + a[mapped.indexOf(i)]},'');
    for( i = 0; i < len; i++) result += text.substr( mapped.indexOf( i), 1);
    return result;  
  }
  
  function encrypt( text, n) {
    var i, len = text.length, mapped = makeMap(len,n), result = "";
    for( i = 0; i < len; i++) result += text.substr( mapped[ i], 1);
    return result;  
  }

  return {
	  encrypt: encrypt
	  ,decrypt: decrypt
  };
}));


var src = "этоттекстзашифрован";
var enc = "экинтесшфаоттарвтзо";
zigzag.decrypt(enc,4);
zigzag.encrypt(src,4);