test.js

function persianToEnglish(value) {
    var newValue = "";
    for (var i = 0; i < value.length; i++) {
        var ch = value.charCodeAt(i);
        if (ch >= 1776 && ch <= 1785) // For Persian digits.
        {
            var newChar = ch - 1728;
            newValue = newValue + String.fromCharCode(newChar);
        }
        else if (ch >= 1632 && ch <= 1641) // For Arabic & Unix digits.
        {
            var newChar = ch - 1584;
            newValue = newValue + String.fromCharCode(newChar);
        }
        else
            newValue = newValue + String.fromCharCode(ch);
    }
    return newValue;
}

function EnglishToPersian(value) {
    var newValue = "";
    for (var i = 0; i < value.length; i++) {
        var ch = value.charCodeAt(i);
        if (ch >= 48 && ch <= 57) // For Persian digits.
        {
            var newChar = ch + 1728;
            newValue = newValue + String.fromCharCode(newChar);
        }
        else if (ch >= 1632 && ch <= 1641) // For Arabic & Unix digits.
        {
            var newChar = ch + 144;
            newValue = newValue + String.fromCharCode(newChar);
        }
        else
            newValue = newValue + String.fromCharCode(ch);
    }
    return newValue;
}

EnglishToPersian("12");