Change configFrom() to configDefinitions()

The main difference is that configFrom returned config key:value pairs, but now configDefinitions returns key:object pairs. Where the object may hold additional flags and methods for each specific config value. Currently the only method included is valueFn() which gets the value from its source. Others will follow.

Additionally:
- Remove `experimental` from configDefinitions/configFrom as it is not used

src/annotator/config/index.js

@@ -3,6 +3,14 @@ import { toBoolean } from '../../shared/type-coercions';
 
 /**
  * @typedef {'sidebar'|'notebook'|'annotator'|'all'} AppContext
+ *
+ * @typedef {import('./settings').SettingsGetters} SettingsGetters
+ *
+ * @typedef ConfigDefinition
+ * @prop {(settings: SettingsGetters) => any} getValue -
+ *   Method to retrieve the value from the incoming source
+ *
+ * @typedef {Record<string, ConfigDefinition>} ConfigDefinitionMap
  */
 
 /**
@@ -60,61 +68,83 @@ function configurationKeys(appContext) {
 }
 
 /**
- * Reads the Hypothesis configuration from the environment.
- *
- * @param {string[]} settingsKeys - List of settings that should be returned.
- * @param {Window} window_ - The Window object to read config from.
+ * Definitions of configuration keys
+ * @type {ConfigDefinitionMap}
  */
-function configFrom(settingsKeys, window_) {
-  const settings = settingsFrom(window_);
-  const allConfigSettings = {
-    annotations: settings.annotations,
-    appType: settings.hostPageSetting('appType', {
+const configDefinitions = {
+  annotations: {
+    getValue: settings => settings.annotations,
+  },
+  appType: {
+    getValue: settings =>
+      settings.hostPageSetting('appType', {
         allowInBrowserExt: true,
       }),
-    branding: settings.hostPageSetting('branding'),
+  },
+  branding: {
+    getValue: settings => settings.hostPageSetting('branding'),
+  },
   // URL of the client's boot script. Used when injecting the client into
   // child iframes.
-    clientUrl: settings.clientUrl,
-    enableExperimentalNewNoteButton: settings.hostPageSetting(
-      'enableExperimentalNewNoteButton'
-    ),
-    experimental: settings.hostPageSetting('experimental', {
-      defaultValue: {},
-    }),
-    group: settings.group,
-    focus: settings.hostPageSetting('focus'),
-    theme: settings.hostPageSetting('theme'),
-    usernameUrl: settings.hostPageSetting('usernameUrl'),
-    onLayoutChange: settings.hostPageSetting('onLayoutChange'),
-    openSidebar: settings.hostPageSetting('openSidebar', {
+  clientUrl: {
+    getValue: settings => settings.clientUrl,
+  },
+  enableExperimentalNewNoteButton: {
+    getValue: settings =>
+      settings.hostPageSetting('enableExperimentalNewNoteButton'),
+  },
+  group: {
+    getValue: settings => settings.group,
+  },
+  focus: {
+    getValue: settings => settings.hostPageSetting('focus'),
+  },
+  theme: {
+    getValue: settings => settings.hostPageSetting('theme'),
+  },
+  usernameUrl: {
+    getValue: settings => settings.hostPageSetting('usernameUrl'),
+  },
+  onLayoutChange: {
+    getValue: settings => settings.hostPageSetting('onLayoutChange'),
+  },
+  openSidebar: {
+    getValue: settings =>
+      settings.hostPageSetting('openSidebar', {
         allowInBrowserExt: true,
-      // Coerce value to a boolean because it may come from via as a string
         coerce: toBoolean,
       }),
-    query: settings.query,
-    requestConfigFromFrame: settings.hostPageSetting('requestConfigFromFrame'),
-    services: settings.hostPageSetting('services'),
-    showHighlights: settings.showHighlights,
-    notebookAppUrl: settings.notebookAppUrl,
-    sidebarAppUrl: settings.sidebarAppUrl,
-    // Subframe identifier given when a frame is being embedded into
+  },
+  query: {
+    getValue: settings => settings.query,
+  },
+  requestConfigFromFrame: {
+    getValue: settings => settings.hostPageSetting('requestConfigFromFrame'),
+  },
+  services: {
+    getValue: settings => settings.hostPageSetting('services'),
+  },
+  showHighlights: {
+    getValue: settings => settings.showHighlights,
+  },
+  notebookAppUrl: {
+    getValue: settings => settings.notebookAppUrl,
+  },
+  sidebarAppUrl: {
+    getValue: settings => settings.sidebarAppUrl,
+  },
+  // Sub-frame identifier given when a frame is being embedded into
   // by a top level client
-    subFrameIdentifier: settings.hostPageSetting('subFrameIdentifier', {
+  subFrameIdentifier: {
+    getValue: settings =>
+      settings.hostPageSetting('subFrameIdentifier', {
         allowInBrowserExt: true,
       }),
-    externalContainerSelector: settings.hostPageSetting(
-      'externalContainerSelector'
-    ),
-  };
-
-  // Only return what we asked for
-  const resultConfig = {};
-  settingsKeys.forEach(key => {
-    resultConfig[key] = allConfigSettings[key];
-  });
-  return resultConfig;
-}
+  },
+  externalContainerSelector: {
+    getValue: settings => settings.hostPageSetting('externalContainerSelector'),
+  },
+};
 
 /**
  * Return the configuration for a given application context.
@@ -122,9 +152,16 @@ function configFrom(settingsKeys, window_) {
  * @param {AppContext} [appContext] - The name of the app.
  */
 export function getConfig(appContext = 'annotator', window_ = window) {
+  const settings = settingsFrom(window_);
+  const config = {};
   // Filter the config based on the application context as some config values
   // may be inappropriate or erroneous for some applications.
-  const filteredKeys = configurationKeys(appContext);
-  const config = configFrom(filteredKeys, window_);
+  let filteredKeys = configurationKeys(appContext);
+  filteredKeys.forEach(name => {
+    const configDef = configDefinitions[name];
+    // Get the value from the configuration source
+    config[name] = configDef.getValue(settings);
+  });
+
   return config;
 }

src/annotator/config/settings.js

@@ -3,6 +3,22 @@ import { parseJsonConfig } from '../../boot/parse-json-config';
 import configFuncSettingsFrom from './config-func-settings-from';
 import isBrowserExtension from './is-browser-extension';
 
+/**
+ * @typedef SettingsGetters
+ * @prop {string|null} annotations
+ * @prop {string|null} query
+ * @prop {string|null} group
+ * @prop {string} showHighlights
+ * @prop {string} clientUrl
+ * @prop {string} sidebarAppUrl
+ * @prop {string} notebookAppUrl
+ 
+ * @prop {(name: string, options?: Object) => (string|null)} hostPageSetting
+ */
+
+/**
+ * @return {SettingsGetters}
+ */
 export default function settingsFrom(window_) {
   const jsonConfigs = parseJsonConfig(window_.document);
   const configFuncSettings = configFuncSettingsFrom(window_);