Validate code with javascript

Hi i have created a code to validate my script but i cant figure out how to make the hphone and fax numeric and "10" digits any suggestions pls

HTML Code:

---

function validate_form ()
{
        valid = true;

        if ( document.input.name.value == "" )
        {
                alert ( "Please enter your name" );
                valid = false;
        }
                               
                                if ( document.input.address.value == "" )
        {
                alert ( "Please enter your address address" );
                valid = false;
        }
               
                                if ( document.input.town.value == "" )
        {
                alert ( "Please enter your Suburb or town" );
                valid = false;
        }
                                  if ( document.input.postcode.value == "" )
        {
                alert ( "Please enter your postocde" );
                valid = false;
        }
                               
                                if ( document.input.hphone.value == "" )
        {
                alert ( "Please enter your home phone number" );
                valid = false;                               
                }               
                                if ( document.input.wphone.value == "" )
        {
                alert ( "Please enter your work phone number" );
                valid = false;
        }
                        if ( document.input.fax.value == "" )
        {
                alert ( "Please enter your fax" );
                valid = false;
        }
       
                if ( document.input.daydropdown.value == "" )
        {
                alert ( "Please enter day for delivery" );
                valid = false;
        }
               
                                if ( document.input.monthdropdown.value == "" )
        {
                alert ( "Please enter month for delivery" );
                valid = false;
        }
                        if ( document.input.yeardropdown.value == "" )
        {
                alert ( "Please enter year of delivery" );
                valid = false;
        }
        {
 var x=document.forms["input"]["email"].value;
 var atpos=x.indexOf("@");
 var dotpos=x.lastIndexOf(".");
 if (atpos<1 || dotpos<atpos+2 || dotpos+2>=x.length)
  {
  alert("Not a valid e-mail address");
  return false;
  }
        }
        return valid;
}
function setVisible(id, visible) {
        var o = document.getElementById(id);
        if (typeof(o) != 'undefined') o.style.visibility = visible ? 'visible' : 'hidden';
        if (typeof(o) == 'undefined') alert("Element with id '" + id + "' not found.");
    }

    function setDisplay(id, visible) {
        var o = document.getElementById(id);
        if (typeof(o) != 'undefined') o.style.display = visible ? 'block' : 'none';
        if (typeof(o) == 'undefined') alert("Element with id '" + id + "' not found.");
    }

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All input values are strings, so you can easily check the 'length' attribute to see how long the strings are.

Code:

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if (document.input.hphone.value.length != 10) { alert("Invalid home phone number"); }

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refreezed has your solution.

I am here just to recommend that you use some existing validation library with all that functionality. jQuery Validate is a good and flexible one. If someone else can recommend others, then do so please.