text输入限制

<input type="text" onkeypress="return keypress(event)"/>

//只能输入数字
 function keypress(e) {
            var keynum;
            if (window.event) // IE
            {
                keynum = e.keyCode;
            }
            else if (e.which) // Netscape/Firefox/Opera
            {
                keynum = e.which;
            }
            if (keynum != 8) {
                var keychar = String.fromCharCode(keynum);
                var numcheck = /\d/;
                return numcheck.test(keychar);
            }
        }