String.reverse and String.translate

string.reverse-and-translate.js

String.prototype.reverse = function() {
  var str='';
  for (i=this.length-1;i>=0;i--) {
    str += this.charAt(i);
  }
  return str;
}

String.prototype.translate = function(from,to) {
  var sl = this.length,
      tl = to.length,
      xlat = new Array(),
      str = '';

  if (sl<1 || tl<1) return this;

  for (i=0; i<256; xlat[i]=i, i++);

  for (i=0; i<tl; i++) {
    xlat[ from.charCodeAt(i) ] = to.charCodeAt(i);
  }

  for (i=0; i<sl; i++) {
    str += String.fromCharCode( xlat[ this.charCodeAt(i) ] );
  }
  return str;
}

var msg = 'Hello world!';

alert(msg.reverse());

alert(msg.translate('lor','gis'));