javascript——数字验证码

<script type="text/javascript">
        function validateCode() {
            var validatevalue = "";
            var codes = new Array(4);
            var colors = new Array("Red", "Green", "Gray", "Blue", "Maroon", "Aqua", "Fuchsia", "Lime", "Olive", "Silver");
            for (var i = 0; i < codes.length; i++) {
                codes[i] = Math.floor(Math.random() * 10);
                validatevalue += codes[i];
            }
            var spans = document.getElementById("divCode").all;
            for (var i = 0; i < spans.length; i++) {
                spans[i].innerText = codes[i];
                spans[i].style.color = colors[Math.floor(Math.random() * 10)];
            }
            document.getElementById("validatevalue").value = validatevalue;
        }

        function validate() {
            if (document.getElementById("textfield3").value != document.getElementById("validatevalue").value) {
                alert("验证码错误");
                validateCode();
                document.getElementById("textfield3").value = "";
                document.getElementById("textfield3").focus();
                return false;
            } else {
                return true;
            }
        }
        document.onload = validateCode();
    </script>