Javascript: Input Field Only Allow Numbers, Backspace and Delete

Using the following javasript in your input field it is posible to restrict the text being entered to numberic values only.

<input type="text" name="quantity[]" value="0" onkeypress="return (event.charCode == 8 || event.charCode == 46 || (event.charCode >= 48 && event.charCode <= 57")) />