Check phone number input and add "-" while allowing delete

buildnumber.js

buildNumber = function() {
  var text = $("#phonenumber").val();
	var new_text = "";

	if( text.length < 3 || (text.length > 3 && text.length < 7) || text.length > 7 ) {
		new_text = text;
	} else if( text.length == 3 || text.length == 7 ) {
		new_text = text + "-";
	}

	$("#phonenumber").val(new_text);
}

$(document).ready(function() {
	$("#phonenumber").on("keydown keyup keypressed",function(event){
        // Allow: backspace, delete, tab, escape, and enter
        if ( event.keyCode == 46 || event.keyCode == 8 || event.keyCode == 9 || event.keyCode == 27 || event.keyCode == 13 || 
             // Allow: Ctrl+A
            (event.keyCode == 65 && event.ctrlKey === true) || 
             // Allow: home, end, left, right
            (event.keyCode >= 35 && event.keyCode <= 39)) {
                 // let it happen, don't do anything
                 return;
        }
        else {
            // Ensure that it is a number and stop the keypress
            if (event.shiftKey || (event.keyCode < 48 || event.keyCode > 57) && (event.keyCode < 96 || event.keyCode > 105 )) {
                event.preventDefault();
            } else {
            	buildNumber();
            }
        }
		
	});
});

/*
//html
<form>
	<input id="phonenumber" type="text" name="number" placeholder="555-555-5555" maxlength="12" />
</form>
*/

// to get number back.

var num = $("#phonenumber").val().replace(/-/g,'');