Send etag as query param (#91)

* sendetagasqueryparam

* comments

* v9.2.0

package.json

@@ -1,6 +1,6 @@
 {
   "name": "configcat-js",
-  "version": "9.1.0",
+  "version": "9.2.0",
   "description": "ConfigCat is a configuration as a service that lets you manage your features and configurations without actually deploying new code.",
   "main": "lib/index.js",
   "types": "lib/index.d.ts",

src/ConfigFetcher.ts

@@ -35,10 +35,16 @@ export class HttpConfigFetcher implements IConfigFetcher {
         httpRequest.onabort = () => reject(new FetchError("abort"));
         httpRequest.onerror = () => reject(new FetchError("failure"));
 
-        httpRequest.open("GET", options.getUrl(), true);
+        let url = options.getUrl();
+        if (lastEtag) {
+          // We are sending the etag as a query parameter so if the browser doesn't automatically adds the If-None-Match header, we can transorm this query param to the header in our CDN provider.
+          url += '&ccetag=' + lastEtag;
+        }
+        httpRequest.open("GET", url, true);
         httpRequest.timeout = options.requestTimeoutMs;
         // NOTE: It's intentional that we don't specify the If-None-Match header.
         // The browser automatically handles it, adding it manually would cause an unnecessary CORS OPTIONS request.
+        // In case the browser doesn't handle it, we are transforming the ccetag query parameter to the If-None-Match header in our CDN provider.
         httpRequest.send(null);
       }
       catch (err) {