align.js

function formatTag(tag){
  var elements = $('content').getElementsBySelector(tag);
  elements.forEach(function(P,index){
    // calculate frequency of characters for the first few characters ( 30 )
    var charCode,
        arabicFreq  = 0,
        englishFreq = 0,
        length = 30,
        parentDir = $(P).getStyle('direction'),
        text = P.innerText;

    for(var i = 0; i < length; i++){
      charCode = text.charCodeAt(i);

      if(1536 < charCode && charCode < 1791){
        // Arabic Script
        arabicFreq++;
      }else if(65 < charCode && charCode < 122){
        // English Script
        englishFreq++;
      }else{
        // Special chars
      }
    }

    if(arabicFreq < englishFreq && parentDir != 'ltr'){
      // English Script in rtl container
      $(P).setStyle({'direction':'ltr'});
    }else if(arabicFreq > englishFreq && parentDir != 'rtl'){
      // Arabic Script in ltr container
      $(P).setStyle({'direction':'rtl'});
    }

  });

}

function align(){

  var tags = ['p','ul','li'];

  tags.forEach(function(tag){
    formatTag(tag);
  });
  
  var textareas = $$('textarea');
  textareas.forEach(function(textarea,index){
    var charCode,arabicFreq = 0,englishFreq = 0;
    Event.observe(textarea,'keyup',function(e){
      var sentence = $(this).value;
      if(sentence.length > 60) return;

      arabicFreq = 0;
      englishFreq = 0;

      for(var i = 0; i < sentence.length; i++){
        charCode = sentence.charCodeAt(i);
        if(1536 < charCode && charCode < 1791){
          // Arabic Script
          arabicFreq++;
        }else if(65 < charCode && charCode < 122){
          // English Script
          englishFreq++;
        }
      }

      // where is the first character of this paragraph?
      if(arabicFreq < englishFreq){
        $(this).setStyle({direction:'ltr'});
      }else{
        $(this).setStyle({direction:'rtl'});
      }
    });
  });

}

Event.observe(window, 'load', align);