How to get return value in Javascript

[Ugat]

Dear Guys,

I have a question about Javascript because I am new in javascript my problem is how to get return true value in my code here my code

<script type="text/javascript" charset="UTF-8" language="javascript">
function numbersonly(myfield, e, dec)
{
	var key;
	var keychar;
	if (window.event)
		key = window.event.keyCode;
	else if (e)
		key = e.which;
	else

		return true;
	keychar = String.fromCharCode(key);
	if ((key==null) || (key==0) || (key==8) || 
		 (key==9) || (key==13) || (key==27) )
function returnnum(){
}

if (window.event)
key= window.event.keyCode;
document.element
else
		return true;
	
	else if ((("01").indexOf(keychar) > -1))
		return true;
	
	else if (dec && (keychar == "."))
		{
		myfield.form.elements[dec].focus();
		return false;
		}
	else
		return false;
}
function checkUncheckAll(theElement) 
{
	var theForm = theElement.form, z = 0;
	for(z=0; z<theForm.length;z++)
	{
		if(theForm[z].type == 'checkbox' && theForm[z].name != 'checkall')
		{
		  theForm[z].checked = theElement.checked;
		}
	}
}

function checkUncheckSome(controller,theElements) 
{
	var formElements = theElements.split(',');
	var theController = document.getElementById(controller);
	for(var z=0; z<formElements.length;z++)
	{
		theItem = document.getElementById(formElements[z]);
		if(theItem.type)
		{
			if (theItem.type=='checkbox') 
			{
				theItem.checked=theController.checked;
			}
		} else {
			theInputs = theItem.getElementsByTagName('input');
			for(var y=0; y<theInputs.length; y++)
			{
				if(theInputs[y].type == 'checkbox' && theInputs[y].id != theController.id)
				{
					theInputs[y].checked = theController.checked;
				}
			}
		}
	}
}
</script>

because my main purpose is to disable other number only 1 and 0 will input if you enter 1 only 1 no other number in one text attach here is my screen shot in the primary is different input box if you enter 1 only and in the second if you enter 0 only will appear do you have idea.

Thanks

[Twey]

<input type="text"
       onkeypress="
         return '01'
             .split()
             .indexOf(String.fromCharCode(event.which || event.keyCode))
           >= 0;
       ">