diff --git a/src/librustdoc/html/static/js/main.js b/src/librustdoc/html/static/js/main.js
index 42cd321849cf..491be052bca2 100644
--- a/src/librustdoc/html/static/js/main.js
+++ b/src/librustdoc/html/static/js/main.js
@@ -231,7 +231,6 @@ function preLoadCss(cssUrl) {
             // When loading settings.html as a standalone page, the equivalent HTML is
             // generated in context.rs.
             setTimeout(() => {
-                // @ts-expect-error
                 const themes = getVar("themes").split(",");
                 for (const theme of themes) {
                     // if there are no themes, do nothing
@@ -415,12 +414,10 @@ function preLoadCss(cssUrl) {
                     }
                     window.StringdexOnload.push(() => {
                         loadScript(
-                            // @ts-expect-error
                             getVar("static-root-path") + getVar("search-js"),
                             sendSearchForm,
                         );
                     });
-                    // @ts-expect-error
                     loadScript(getVar("static-root-path") + getVar("stringdex-js"), sendSearchForm);
                     loadScript(resourcePath("search.index/root", ".js"), sendSearchForm);
                 }
@@ -622,8 +619,7 @@ function preLoadCss(cssUrl) {
      */
     function openParentDetails(elem) {
         while (elem) {
-            if (elem.tagName === "DETAILS") {
-                // @ts-expect-error
+            if (elem instanceof HTMLDetailsElement) {
                 elem.open = true;
             }
             elem = elem.parentElement;
@@ -659,10 +655,8 @@ function preLoadCss(cssUrl) {
         }
 
         if (document.activeElement &&
-            document.activeElement.tagName === "INPUT" &&
-            // @ts-expect-error
+            document.activeElement instanceof HTMLInputElement &&
             document.activeElement.type !== "checkbox" &&
-            // @ts-expect-error
             document.activeElement.type !== "radio") {
             switch (getVirtualKey(ev)) {
             case "Escape":
@@ -969,19 +963,19 @@ function preLoadCss(cssUrl) {
         const selfPath = script ? script.getAttribute("data-self-path") : null;
 
         // These sidebar blocks need filled in, too.
-        const mainContent = document.querySelector("#main-content");
-        const sidebarSection = document.querySelector(".sidebar section");
+        const mainContent = nonnull(document.querySelector("#main-content"));
+        const sidebarSection = nonnull(document.querySelector(".sidebar section"));
         let methods = document.querySelector(".sidebar .block.method");
         let associatedTypes = document.querySelector(".sidebar .block.associatedtype");
         let associatedConstants = document.querySelector(".sidebar .block.associatedconstant");
         let sidebarTraitList = document.querySelector(".sidebar .block.trait-implementation");
 
-        // @ts-expect-error
-        for (const impList of imp[window.currentCrate]) {
+        for (const impList of imp[nonnull(window.currentCrate)]) {
             const types = impList.slice(2);
             const text = impList[0];
-            const isTrait = impList[1] !== 0;
             const traitName = impList[1];
+            const isTrait = typeof traitName === "string";
+            // @ts-expect-error
             if (types.indexOf(selfPath) === -1) {
                 continue;
             }
@@ -1005,28 +999,19 @@ function preLoadCss(cssUrl) {
                     h.appendChild(link);
                     trait_implementations = outputList;
                     trait_implementations_header = outputListHeader;
-                    // @ts-expect-error
                     sidebarSection.appendChild(h);
                     sidebarTraitList = document.createElement("ul");
                     sidebarTraitList.className = "block trait-implementation";
-                    // @ts-expect-error
                     sidebarSection.appendChild(sidebarTraitList);
-                    // @ts-expect-error
                     mainContent.appendChild(outputListHeader);
-                    // @ts-expect-error
                     mainContent.appendChild(outputList);
                 } else {
                     implementations = outputList;
                     if (trait_implementations) {
-                        // @ts-expect-error
                         mainContent.insertBefore(outputListHeader, trait_implementations_header);
-                        // @ts-expect-error
                         mainContent.insertBefore(outputList, trait_implementations_header);
                     } else {
-                        const mainContent = document.querySelector("#main-content");
-                        // @ts-expect-error
                         mainContent.appendChild(outputListHeader);
-                        // @ts-expect-error
                         mainContent.appendChild(outputList);
                     }
                 }
@@ -1071,8 +1056,7 @@ function preLoadCss(cssUrl) {
             if (isTrait) {
                 const li = document.createElement("li");
                 const a = document.createElement("a");
-                // @ts-expect-error
-                a.href = `#${template.content.querySelector(".impl").id}`;
+                a.href = `#${nonnull(template.content.querySelector(".impl")).id}`;
                 a.textContent = traitName;
                 li.appendChild(a);
                 // @ts-expect-error
@@ -1099,14 +1083,10 @@ function preLoadCss(cssUrl) {
                         const insertionReference = methods || sidebarTraitList;
                         if (insertionReference) {
                             const insertionReferenceH = insertionReference.previousElementSibling;
-                            // @ts-expect-error
                             sidebarSection.insertBefore(blockHeader, insertionReferenceH);
-                            // @ts-expect-error
                             sidebarSection.insertBefore(block, insertionReferenceH);
                         } else {
-                            // @ts-expect-error
                             sidebarSection.appendChild(blockHeader);
-                            // @ts-expect-error
                             sidebarSection.appendChild(block);
                         }
                         if (hasClass(item, "associatedtype")) {
diff --git a/src/librustdoc/html/static/js/rustdoc.d.ts b/src/librustdoc/html/static/js/rustdoc.d.ts
index 555324c16f71..3857e6e9fd87 100644
--- a/src/librustdoc/html/static/js/rustdoc.d.ts
+++ b/src/librustdoc/html/static/js/rustdoc.d.ts
@@ -526,7 +526,8 @@ declare namespace rustdoc {
     }
 
     type TypeImpls = {
-        [cratename: string]: Array<Array<string|0>>
+        /* [text, traitName (0 if not a trait), ...types] */
+        [cratename: string]: Array<[string, string|0, ...string[]]>
     }
 
     /**
@@ -578,4 +579,16 @@ declare namespace rustdoc {
         "typeNameIdOfHof": number,
         "typeNameIdOfNever": number,
     };
+
+    type VarName = "name"
+        | "root-path"
+        | "static-root-path"
+        | "current-crate"
+        | "themes"
+        | "resource-suffix"
+        | "rustdoc-version"
+        | "channel"
+        | "search-js"
+        | "stringdex-js"
+        | "settings-js";
 }
diff --git a/src/librustdoc/html/static/js/storage.js b/src/librustdoc/html/static/js/storage.js
index 1ec7cb4ced06..29b94ea424e2 100644
--- a/src/librustdoc/html/static/js/storage.js
+++ b/src/librustdoc/html/static/js/storage.js
@@ -199,12 +199,16 @@ function getCurrentValue(name) {
  * Get a value from the rustdoc-vars div, which is used to convey data from
  * Rust to the JS. If there is no such element, return null.
  *
- * @param {string} name
- * @returns {string|null}
+ * @param {rustdoc.VarName} name
+ * @returns {string}
  */
 function getVar(name) {
     const el = document.querySelector("head > meta[name='rustdoc-vars']");
-    return el ? el.getAttribute("data-" + name) : null;
+    const v = el ? el.getAttribute("data-" + name) : null;
+    if (v !== null) {
+        return v;
+    }
+    throw `rustdoc var "${name}" is missing`;
 }
 
 /**
@@ -294,6 +298,8 @@ const updateTheme = (function() {
     return updateTheme;
 })();
 
+// typescript thinks we're forgetting to call window.matchMedia,
+// but we're checking browser support of media queries.
 // @ts-ignore
 if (getSettingValue("use-system-theme") !== "false" && window.matchMedia) {
     // update the preferred dark theme if the user is already using a dark theme