add storage object to provide utilities for localstore

Author: bnmnetp

runestone/common/js/bookfuncs.js

@@ -1137,3 +1137,34 @@ function injectCodeCoach(div_id) {
                      'div_id': div_id
                  });
 }
+
+var storage = {
+    set: function(directive, value) {
+        localStorage.setItem(directive+"_value", value);
+        localStorage.setItem(directive+"_timestamp", $.now());
+    },
+    remove: function(directive) {
+        localStorage.removeItem(directive+"_value");
+        localStorage.removeItem(directive+"_timestamp");
+    },
+    get: function(directive) {
+        return localStorage.getItem(directive+"_value");
+    },
+    has: function(directive) {
+        return localStorage.getItem(directive+"_value") !== null;
+    },
+    // Tests whether the server has the newer version
+    is_new: function(directive, server_time) {
+        var stored_time = localStorage.getItem(directive+"_timestamp");
+        return (server_time >= stored_time+5000);
+    },
+};
+
+var timers = {};
+function addDelay(directive, action, delay) {
+    if (delay === undefined) {
+        delay = 400;
+    }
+    clearTimeout(timers[directive]);
+    timers[directive] = setTimeout(action, delay);
+}