diff --git a/.eslintrc.yml b/.eslintrc.yml
index 3d2e1c34..3c65ee95 100644
--- a/.eslintrc.yml
+++ b/.eslintrc.yml
@@ -171,7 +171,7 @@ rules:
   no-loss-of-precision: error
   no-misleading-character-class: error
   no-obj-calls: error
-  no-promise-executor-return: off # TODO
+  no-promise-executor-return: error
   no-prototype-builtins: error
   no-regex-spaces: error
   no-setter-return: error
@@ -256,7 +256,7 @@ rules:
   no-void: error
   no-warning-comments: off
   no-with: error
-  prefer-named-capture-group: off # ES2018
+  prefer-named-capture-group: error
   prefer-promise-reject-errors: error
   prefer-regex-literals: error
   radix: error
@@ -322,7 +322,7 @@ rules:
   no-restricted-syntax: off
   no-tabs: error
   no-ternary: off
-  no-underscore-dangle: off # TODO
+  no-underscore-dangle: error
   no-unneeded-ternary: error
   one-var: [error, never]
   operator-assignment: error
@@ -503,9 +503,9 @@ overrides:
       '@typescript-eslint/no-var-requires': error
       '@typescript-eslint/prefer-as-const': off # TODO consider
       '@typescript-eslint/prefer-enum-initializers': off # TODO consider
-      '@typescript-eslint/prefer-for-of': off # TODO switch to error after TS migration
+      '@typescript-eslint/prefer-for-of': error
       '@typescript-eslint/prefer-function-type': error
-      '@typescript-eslint/prefer-includes': off # TODO switch to error after IE11 drop
+      '@typescript-eslint/prefer-includes': error
       '@typescript-eslint/prefer-literal-enum-member': error
       '@typescript-eslint/prefer-namespace-keyword': error
       '@typescript-eslint/prefer-nullish-coalescing': error
@@ -515,13 +515,13 @@ overrides:
       '@typescript-eslint/prefer-reduce-type-parameter': error
       '@typescript-eslint/prefer-regexp-exec': error
       '@typescript-eslint/prefer-ts-expect-error': error
-      '@typescript-eslint/prefer-string-starts-ends-with': off # TODO switch to error after IE11 drop
+      '@typescript-eslint/prefer-string-starts-ends-with': error
       '@typescript-eslint/promise-function-async': off
       '@typescript-eslint/require-array-sort-compare': error
       '@typescript-eslint/restrict-plus-operands':
         [error, { checkCompoundAssignments: true }]
       '@typescript-eslint/restrict-template-expressions': error
-      '@typescript-eslint/strict-boolean-expressions': off # TODO consider
+      '@typescript-eslint/strict-boolean-expressions': error
       '@typescript-eslint/switch-exhaustiveness-check': error
       '@typescript-eslint/triple-slash-reference': error
       '@typescript-eslint/typedef': off
diff --git a/resources/build-npm.js b/resources/build-npm.js
index a3a9217e..4cc27d2e 100644
--- a/resources/build-npm.js
+++ b/resources/build-npm.js
@@ -52,12 +52,12 @@ function buildPackageJSON() {
   delete packageJSON.devDependencies;
 
   const { version } = packageJSON;
-  const versionMatch = /^\d+\.\d+\.\d+-?(.*)?$/.exec(version);
+  const versionMatch = /^\d+\.\d+\.\d+-?(?<preReleaseTag>.*)?$/.exec(version);
   if (!versionMatch) {
     throw new Error('Version does not match semver spec: ' + version);
   }
 
-  const [, preReleaseTag] = versionMatch;
+  const { preReleaseTag } = versionMatch.groups;
 
   if (preReleaseTag != null) {
     const [tag] = preReleaseTag.split('.');
diff --git a/resources/gen-changelog.js b/resources/gen-changelog.js
index 7449c179..48a3cf36 100644
--- a/resources/gen-changelog.js
+++ b/resources/gen-changelog.js
@@ -47,14 +47,14 @@ if (!packageJSON.repository || typeof packageJSON.repository.url !== 'string') {
   process.exit(1);
 }
 
-const repoURLMatch = /https:\/\/github.com\/([^/]+)\/([^/]+).git/.exec(
+const repoURLMatch = /https:\/\/github.com\/(?<githubOrg>[^/]+)\/(?<githubRepo>[^/]+).git/.exec(
   packageJSON.repository.url,
 );
 if (repoURLMatch == null) {
   console.error('Cannot extract organization and repo name from repo URL!');
   process.exit(1);
 }
-const [, githubOrg, githubRepo] = repoURLMatch;
+const { githubOrg, githubRepo } = repoURLMatch.groups;
 
 getChangeLog()
   .then((changelog) => process.stdout.write(changelog))
@@ -275,9 +275,9 @@ function commitsInfoToPRs(commits) {
       (pr) => pr.repository.nameWithOwner === `${githubOrg}/${githubRepo}`,
     );
     if (associatedPRs.length === 0) {
-      const match = / \(#([0-9]+)\)$/m.exec(commit.message);
+      const match = / \(#(?<prNumber>[0-9]+)\)$/m.exec(commit.message);
       if (match) {
-        prs[parseInt(match[1], 10)] = true;
+        prs[parseInt(match.groups.prNumber, 10)] = true;
         continue;
       }
       throw new Error(
diff --git a/src/index.ts b/src/index.ts
index 23b4d930..a185ff99 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -186,7 +186,7 @@ type Middleware = (request: Request, response: Response) => Promise<void>;
  * configure behavior, and returns an express middleware.
  */
 export function graphqlHTTP(options: Options): Middleware {
-  if (!options) {
+  if (options == null) {
     throw new Error('GraphQL middleware requires options.');
   }
 
diff --git a/src/parseBody.ts b/src/parseBody.ts
index 32b1f968..3cac4c3d 100644
--- a/src/parseBody.ts
+++ b/src/parseBody.ts
@@ -83,7 +83,7 @@ async function readBody(
   const charset = typeInfo.parameters.charset?.toLowerCase() ?? 'utf-8';
 
   // Assert charset encoding per JSON RFC 7159 sec 8.1
-  if (charset.slice(0, 4) !== 'utf-') {
+  if (!charset.startsWith('utf-')) {
     throw httpError(415, `Unsupported charset "${charset.toUpperCase()}".`);
   }