Here is my solution:
function InputValidator(input, validationType, validChars) {
if (input === null || input.nodeType !== 1 || input.type !== 'text' && input.type !== 'number')
    throw ('Please specify a valid input');
if (!(InputValidator.ValidationType.hasOwnProperty(validationType) || validationType))
    throw 'Please specify a valid Validation type';
input.InputValidator = this;
input.InputValidator.ValidCodes = [];
input.InputValidator.ValidCodes.Add = function (item) {
    this[this.length] = item;
};
input.InputValidator.ValidCodes.hasValue = function (value, target) {
    var i;
    for (i = 0; i < this.length; i++) {
        if (typeof (target) === 'undefined') {
            if (this[i] === value)
                return true;
        }
        else {
            if (this[i][target] === value)
                return true;
        }
    }
    return false;
};
var commandKeys = {
    'backspace': 8,
    'tab': 9,
    'enter': 13,
    'shift': 16,
    'ctrl': 17,
    'alt': 18,
    'pause/break': 19,
    'caps lock': 20,
    'escape': 27,
    'page up': 33,
    'page down': 34,
    'end': 35,
    'home': 36,
    'left arrow': 37,
    'up arrow': 38,
    'right arrow': 39,
    'down arrow': 40,
    'insert': 45,
    'delete': 46,
    'left window key': 91,
    'right window key': 92,
    'select key': 93,
    /*creates Confusion in IE */
    //'f1': 112,
    //'f2': 113,
    //'f3': 114,
    //'f4': 115,
    //'f5': 116,
    //'f6': 117,
    //'f7': 118,
    //'f8': 119,
    //'f9': 120,
    //'f10': 121,
    //'f11': 122,
    //'f12': 123,
    'num lock': 144,
    'scroll lock': 145,
};
commandKeys.hasValue = function (value) {
    for (var a in this) {
        if (this[a] === value)
            return true;
    }
    return false;
};
function getCharCodes(arrTarget, chars) {
    for (var i = 0; i < chars.length; i++) {
        arrTarget.Add(chars[i].charCodeAt(0));
    }
}
function triggerEvent(name, element) {
    if (document.createEventObject) {
        // dispatch for IE
        var evt = document.createEventObject();
        return element.fireEvent('on' + name, evt)
    }
    else {
        // dispatch for firefox + others
        var evt = document.createEvent("HTMLEvents");
        evt.initEvent(name, true, true); // event type,bubbling,cancelable
        return !element.dispatchEvent(evt);
    }
}
if (validationType == InputValidator.ValidationType.Custom) {
    if (typeof (validChars) === 'undefined')
        throw 'Please add valid characters';
    getCharCodes(input.InputValidator.ValidCodes, validChars);
}
else if (validationType == InputValidator.ValidationType.Decimal) {
    getCharCodes(input.InputValidator.ValidCodes, '0123456789.');
}
else if (validationType == InputValidator.ValidationType.Numeric) {
    getCharCodes(input.InputValidator.ValidCodes, '0123456789');
}
input.InputValidator.ValidateChar = function (c) {
    return this.ValidCodes.hasValue(c.charCodeAt(0));
}
input.InputValidator.ValidateString = function (s) {
    var arr = s.split('');
    for (var i = 0; i < arr.length; i++) {
        if (!this.ValidateChar(arr[i])) {
            arr[i] = '';
        }
    }
    return arr.join('');
}
function bindEvent(el, eventName, eventHandler) {
    if (el.addEventListener) {
        el.addEventListener(eventName, eventHandler, false);
    } else if (el.attachEvent) {
        el.attachEvent('on' + eventName, eventHandler);
    }
}
function getCaretPosition(i) {
    if (!i) return;
    if ('selectionStart' in i) {
        return i.selectionStart;
    }
    else {
        if (document.selection) {
            var sel = document.selection.createRange();
            var selLen = document.selection.createRange().text.length;
            sel.moveStart('character', -i.value.length);
            return sel.text.length - selLen;
        }
    }
}
function setCursor(node, pos) {
    var node = (typeof (node) === "string" || node instanceof String) ? document.getElementById(node) : node;
    if (!node) {
        return false;
    }
    else if (node.createTextRange) {
        var textRange = node.createTextRange();
        textRange.collapse(true);
        textRange.moveEnd(pos);
        textRange.moveStart(pos);
        textRange.select();
        return true;
    } else if (node.setSelectionRange) {
        node.setSelectionRange(pos, pos);
        return true;
    }
    return false;
}
function validateActive() {
    if (input.isActive) {
        var pos = getCaretPosition(input);
        var arr = input.value.split('');
        for (var i = 0; i < arr.length; i++) {
            if (!this.ValidateChar(arr[i])) {
                arr[i] = '';
                if (pos > i)
                    pos--;
            }
        }
        console.log('before : ' + input.value);
        input.value = arr.join('');
        console.log('after : ' + input.value, input);
        setCursor(input, pos);
        setTimeout(validateActive, 10);
    }
}
bindEvent(input, 'keypress', function (e) {
    var evt = e || window.event;
    var charCode = evt.which || evt.keyCode;
    if (!input.InputValidator.ValidCodes.hasValue(charCode) && !commandKeys.hasValue(charCode)) {
        if (evt.preventDefault) {
            evt.preventDefault();
            evt.stopPropagation();
        }
        return false;
    }
});
bindEvent(input, 'keyup', function (e) {
    var evt = e || window.event;
    var charCode = evt.which || evt.keyCode;
    if (!input.InputValidator.ValidCodes.hasValue(charCode) && !commandKeys.hasValue(charCode)) {
        if (evt.preventDefault) {
            evt.preventDefault();
            evt.stopPropagation();
        }
        return false;
    }
});
bindEvent(input, 'change', function (e) {
    var dt = input.value;
    input.value = input.InputValidator.ValidateString(input.value);
    if (input.value !== dt)
        triggerEvent('change', input);
});
bindEvent(input, 'blur', function (e) {
    var dt = input.value;
    input.value = input.InputValidator.ValidateString(input.value);
    input.isActive = false;
    if (input.value !== dt)
        triggerEvent('blur', input);
});
bindEvent(input, 'paste', function (e) {
    var evt = e || window.event;
    var svt = input.value;
    if (evt && evt.clipboardData && evt.clipboardData.getData) {// Webkit - get data from clipboard, put into editdiv, cleanup, then cancel event
        if (/text\/html/.test(evt.clipboardData.types)) {
            var dt = evt.clipboardData.getData('text/html');
            input.value = input.InputValidator.ValidateString(dt);
            if (input.value !== dt)
                triggerEvent('change', input);
        }
        else if (/text\/plain/.test(e.clipboardData.types)) {
            var dt = evt.clipboardData.getData('text/plain');
            input.value = input.InputValidator.ValidateString(dt);
            if (input.value !== dt)
                triggerEvent('change', input);
        }
        else {
            input.value = '';
        }
        waitforpastedata(input, svt);
        if (e.preventDefault) {
            e.stopPropagation();
            e.preventDefault();
        }
        return false;
    }
    else {// Everything else - empty editdiv and allow browser to paste content into it, then cleanup
        input.value = '';
        waitforpastedata(input, svt);
        return true;
    }
});
bindEvent(input, 'select', function (e) {
    var evt = e || window.event;
    if (evt.preventDefault) {
        evt.preventDefault();
        evt.stopPropagation();
    }
    return false;
});
bindEvent(input, 'selectstart', function (e) {
    var evt = e || window.event;
    if (evt.preventDefault) {
        evt.preventDefault();
        evt.stopPropagation();
    }
    return false;
});
/* no need to validate wile active,
   removing F keys fixed IE compatability*/
//bindEvent(input, 'fucus', function (e) {
//    input.isActive = true;
//    validateActive();
//});
//validate current value of the textbox
{
    var dt = input.value;
    input.value = input.InputValidator.ValidateString(input.value);
    //trigger event to indicate value has changed
    if (input.value !== dt)
        triggerEvent('change', input);
}
function waitforpastedata(elem, savedcontent) {
    if (elem.value !== '') {
        var dt = input.value;
        elem.value = elem.InputValidator.ValidateString(elem.value);
        if (input.value !== dt)
            triggerEvent('change', input);
    }
    else {
        var that = {
            e: elem,
            s: savedcontent
        }
        that.callself = function () {
            waitforpastedata(that.e, that.s)
        }
        setTimeout(that.callself, 10);
    }
}
}
InputValidator.ValidationType = new (function (types) {
    for (var i = 0; i < types.length; i++) {
        this[types[i]] = types[i];
    }
})(['Numeric', 'Custom', 'Decimal']);
To apply it to an input, do the following :
new InputValidator(document.getElementById('txtValidate'), InputValidator.ValidationType.Decimal);/* Numeric or Custom */
If you specify Custom as the validation type you have to specify the valid characters.
eg : 
new InputValidator(document.getElementById('txtValidate'), InputValidator.ValidationType.Custom,'1234abc');