Validate Number JS

//Validate Number
/*Only Numbers are allowed. The argument number is the id of textbox. checkRequired means the field is necessary or not
(necessary maens true otherwise false). The argument checkLength means to check the length of the
number against the size. We must send the size if we send checkLength as true otherwise not necessary*/
function ValidateNumber(textElement, checkRequired, checkLength, size,spanID,controlName)
{
document.getElementById(spanID).innerHTML='';
textElement=document.getElementById(textElement);
var num = textElement.value;
var format = /^[0-9]+$/;
if(checkRequired == true)
{
if(num == "" num == '' num == null)
{
document.getElementById(spanID).innerHTML= controlName+' is required';
return false;
}
else
{
if(num.match(format))
{
if(checkLength == true)
{
if(num.length > size)
{
document.getElementById(spanID).innerHTML= 'Maximum is '+ size +' digits';
return false;
}
else
{
return true;
}
}
else
{
return true;
}
}
else
{
document.getElementById(spanID).innerHTML= 'Invalid Number';
return false;
}
}
}
else
{
if(num == "" num == '' num == null)
{
return true;
}
else
{
if(num.match(format))
{
if(checkLength == true)
{
if(num.length > size)
{
document.getElementById(spanID).innerHTML= 'Maximum is '+ size + ' digits';
return false;
}
else
{
return true;
}
}
else
{
return true;
}
}
else
{
document.getElementById(spanID).innerHTML= 'Invalid Number';
return false;
}
}
}
}