This is a little plugin I wrote to ensure form fields only accept numbers as input

jq.numbersOnlyField.js

$.fn.numbersOnlyField = function() {
  var element = this,
		validKeys = [48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 8, 9],
		currentValue;
	function onkeydown_field(e) {
		currentValue = element.val();	
	}
	function onkeyup_field(e) {
		var value = element.val();
		if (/[\d]+$/g.test(value)) {
			if (validKeys.indexOf(e.keyCode) < 0) {
				element.val(currentValue);
			}
		} else {
			element.val('');
		}
		 
	}
	element.on('keyup', onkeyup_field);
	element.on('keydown', onkeydown_field);
}