Started on node.js+socket.io+mongoDB on the backend for more responsivnes

server/node_modules/express/node_modules/fresh/index.js

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+
+/**
+ * Expose `fresh()`.
+ */
+
+module.exports = fresh;
+
+/**
+ * Check freshness of `req` and `res` headers.
+ *
+ * When the cache is "fresh" __true__ is returned,
+ * otherwise __false__ is returned to indicate that
+ * the cache is now stale.
+ *
+ * @param {Object} req
+ * @param {Object} res
+ * @return {Boolean}
+ * @api public
+ */
+
+function fresh(req, res) {
+  // defaults
+  var etagMatches = true;
+  var notModified = true;
+
+  // fields
+  var modifiedSince = req['if-modified-since'];
+  var noneMatch = req['if-none-match'];
+  var lastModified = res['last-modified'];
+  var etag = res['etag'];
+  var cc = req['cache-control'];
+
+  // unconditional request
+  if (!modifiedSince && !noneMatch) return false;
+
+  // check for no-cache cache request directive
+  if (cc && cc.indexOf('no-cache') !== -1) return false;  
+
+  // parse if-none-match
+  if (noneMatch) noneMatch = noneMatch.split(/ *, */);
+
+  // if-none-match
+  if (noneMatch) etagMatches = ~noneMatch.indexOf(etag) || '*' == noneMatch[0];
+
+  // if-modified-since
+  if (modifiedSince) {
+    modifiedSince = new Date(modifiedSince);
+    lastModified = new Date(lastModified);
+    notModified = lastModified <= modifiedSince;
+  }
+
+  return !! (etagMatches && notModified);
+}