ajax: MDL-17084 provide a way for JavaScript to update user preferences.

lib/javascript-static.js

@@ -553,4 +553,39 @@ emoticons_help = {
         }
         emoticons_help.inputarea.focus();
     }
+}
+
+/**
+ * Makes a best effort to connect back to Moodle to update a user preference,
+ * however, there is no mechanism for finding out if the update succeeded.
+ *
+ * Before you can use this function in your JavsScript, you must have called
+ * user_preference_allow_ajax_update from moodlelib.php to tell Moodle that
+ * the udpate is allowed, and how to safely clean and submitted values.
+ *
+ * @param String name the name of the setting to udpate.
+ * @param String the value to set it to.
+ */
+function set_user_preference(name, value) {
+    // Don't generate a script error if the library has not been loaded,
+    // unless we are a Developer, in which case we want the error.
+    if (YAHOO && YAHOO.util && YAHOO.util.Connect || moodle_cfg.developerdebug) {
+        var url = moodle_cfg.wwwroot + '/lib/ajax/setuserpref.php?sesskey=' +
+                moodle_cfg.sesskey + '&pref=' + encodeURI(name) + '&value=' + encodeURI(value);
+
+        // If we are a developer, ensure that failures are reported.
+        var callback = {};
+        if (moodle_cfg.developerdebug) {
+            callback.failure = function() {
+                var a = document.createElement('a');
+                a.href = url;
+                a.classname = 'error';
+                a.appendChild(document.createTextNode("Error updating user preference '" + name + "' using ajax. Clicking this link will repeat the Ajax call that failed so you can see the error."));
+                document.body.insertBefore(a, document.body.firstChild);
+            }
+        }
+
+        // Make the request.
+        YAHOO.util.Connect.asyncRequest('GET', url, callback); 
+    }
 }