304 CORS_html/css_WEB-ITnose

304响应， cors问题: 没有 access-control-allow-origin 这个头信息时，以前次返回的200请求为准。

示例：可能已被删除
http://7af3zm.com1.z0.glb.clouddn.com/ajax_304_cors.html

附上源码：
html

// var _ajax_34re = false;function getAjax () {var _ajax_34re = false;if (_ajax_34re) {return _ajax_34re;}try {_ajax_34re = new XMLHttpRequest();   } catch (trymicrosoft) {     try {_ajax_34re = new ActiveXObject("Msxml2.XMLHTTP");     } catch (othermicrosoft) {       try {_ajax_34re = new ActiveXObject("Microsoft.XMLHTTP");       } catch (failed) {_ajax_34re = false;       }     }   }return _ajax_34re;}function load(url) {request =  getAjax ();request.open("GET", url);    request.onreadystatechange = updatePage;    request.send(null);   }   function updatePage() {     if (request.readyState == 4)       if (request.status == 200)         alert("Server is done!" + request.responseText);       else if (request.status == 404)         alert("Request URL does not exist");       else         alert("Error: status code is " + request.status);   }
access: 200、304响应都有 Access-Control-Allow-Origin:*;access-non: 200、304响应都 没 有 Access-Control-Allow-Origin;access-200: 200响应都有 Access-Control-Allow-Origin:*, 304响应 没 有 Access-Control-Allow-Origin;
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clojure
(ns base-web.handler  (:require [compojure.core :refer :all]            [compojure.route :as route]            [ring.middleware.defaults :refer [wrap-defaults site-defaults]]            [clojure.pprint :as log]))(def my-route    (-> site-defaults        (assoc-in [:security :anti-forgery] false)        (assoc-in [:params] false)        ))(defn print-req [req]    (println )    (log/pprint my-route)    (log/pprint req)    (log/pprint (slurp (:body req)))    (println "done"))(defn access-200 [req]    (let [etag "e-access-200"]    (if (not= etag (get-in req [:headers "if-none-match"]))        (do (println "200")            {:status 200,             :headers {"Content-Type" "application/json", "Access-Control-Allow-Origin" "*", "ETag" etag}             :body "{\"success\":true, \"frame\": \"ring\"}"})         (do (println "304")            {:status 304,                :headers {"Content-Type" "application/json", "ETag" etag}}))))(defn access-non [req]    (let [etag "e-access-non"]    (if (not= etag (get-in req [:headers "if-none-match"]))        (do (println "200")            {:status 200,             :headers {"Content-Type" "application/json", "ETag" etag}             :body "{\"success\":true, \"frame\": \"ring\"}"})         (do (println "304")            {:status 304,                :headers {"Content-Type" "application/json", "ETag" etag}}))))(defn access [req]    (let [etag "e-access"]    (if (not= etag (get-in req [:headers "if-none-match"]))        (do (println "200")            {:status 200,             :headers {"Content-Type" "application/json", "Access-Control-Allow-Origin" "*", "ETag" etag}             :body "{\"success\":true, \"frame\": \"ring\"}"})         (do (println "304")            {:status 304,                :headers {"Content-Type" "application/json", "ETag" etag}}))))(defroutes app-routes  (GET "/access-200" req (access-200 req) )  (GET "/access-non" req (access-non req) )  (GET "/access" req (access req) )  (ANY "*" req    (print-req req)    "{\"success\":true, \"frame\": \"compojure\"}")  (route/not-found "Not Found"))(def app  (wrap-defaults app-routes my-route));; lein ring server []
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