rustdoc: clean up storage.js

This converts a few functions to more compact versions of
themselves, and moves `RUSTDOC_MOBILE_BREAKPOINT` to main.js where
it's actually used.

src/librustdoc/html/static/css/rustdoc.css

@@ -1538,7 +1538,7 @@ However, it's not needed with smaller screen width because the doc/code block is
 /*
 WARNING: RUSTDOC_MOBILE_BREAKPOINT MEDIA QUERY
 If you update this line, then you also need to update the line with the same warning
-in storage.js
+in main.js
 */
 @media (max-width: 700px) {
 	/* When linking to an item with an `id` (for instance, by clicking a link in the sidebar,

src/librustdoc/html/static/js/main.js

@@ -4,6 +4,11 @@
 
 "use strict";
 
+// WARNING: RUSTDOC_MOBILE_BREAKPOINT MEDIA QUERY
+// If you update this line, then you also need to update the media query with the same
+// warning in rustdoc.css
+window.RUSTDOC_MOBILE_BREAKPOINT = 700;
+
 // Given a basename (e.g. "storage") and an extension (e.g. ".js"), return a URL
 // for a resource under the root-path, with the resource-suffix.
 function resourcePath(basename, extension) {

src/librustdoc/html/static/js/storage.js

@@ -8,29 +8,14 @@
 const darkThemes = ["dark", "ayu"];
 window.currentTheme = document.getElementById("themeStyle");
 
-// WARNING: RUSTDOC_MOBILE_BREAKPOINT MEDIA QUERY
-// If you update this line, then you also need to update the media query with the same
-// warning in rustdoc.css
-window.RUSTDOC_MOBILE_BREAKPOINT = 700;
-
 const settingsDataset = (function() {
     const settingsElement = document.getElementById("default-settings");
-    if (settingsElement === null) {
+    return settingsElement && settingsElement.dataset ? settingsElement.dataset : null;
-        return null;
-    }
-    const dataset = settingsElement.dataset;
-    if (dataset === undefined) {
-        return null;
-    }
-    return dataset;
 })();
 
 function getSettingValue(settingName) {
     const current = getCurrentValue(settingName);
-    if (current !== null) {
+    if (current === null && settingsDataset !== null) {
-        return current;
-    }
-    if (settingsDataset !== null) {
         // See the comment for `default_settings.into_iter()` etc. in
         // `Options::from_matches` in `librustdoc/config.rs`.
         const def = settingsDataset[settingName.replace(/-/g,"_")];
@@ -38,7 +23,7 @@ function getSettingValue(settingName) {
             return def;
         }
     }
-    return null;
+    return current;
 }
 
 const localStoredTheme = getSettingValue("theme");
@@ -49,19 +34,17 @@ function hasClass(elem, className) {
 }
 
 function addClass(elem, className) {
-    if (!elem || !elem.classList) {
+    if (elem && elem.classList) {
-        return;
-    }
         elem.classList.add(className);
     }
+}
 
 // eslint-disable-next-line no-unused-vars
 function removeClass(elem, className) {
-    if (!elem || !elem.classList) {
+    if (elem && elem.classList) {
-        return;
-    }
         elem.classList.remove(className);
     }
+}
 
 /**
  * Run a callback for every element of an Array.
@@ -127,11 +110,7 @@ function getCurrentValue(name) {
 // Rust to the JS. If there is no such element, return null.
 const getVar = (function getVar(name) {
     const el = document.getElementById("rustdoc-vars");
-    if (el) {
+    return el ? el.attributes["data-" + name].value : null;
-        return el.attributes["data-" + name].value;
-    } else {
-        return null;
-    }
 });
 
 function switchTheme(newThemeName, saveTheme) {