diff --git a/lib/regexpu-core.d.ts b/lib/regexpu-core.d.ts
new file mode 100644
index 000000000000..415800a5196c
--- /dev/null
+++ b/lib/regexpu-core.d.ts
@@ -0,0 +1,17 @@
+declare module "regexpu-core" {
+  type RegexpuOptions = {
+    unicodeFlag?: "transform" | false;
+    unicodeSetsFlag?: "transform" | "parse" | false;
+    dotAllFlag?: "transform" | false;
+    unicodePropertyEscapes?: "transform" | false;
+    namedGroups?: "transform" | false;
+    onNamedGroup?: (name: string, index: number) => void;
+  };
+  function rewritePattern(
+    pattern: string,
+    flags: string,
+    options: RegexpuOptions
+  ): string;
+  export = rewritePattern;
+  export { RegexpuOptions };
+}
diff --git a/packages/babel-core/src/config/helpers/config-api.ts b/packages/babel-core/src/config/helpers/config-api.ts
index 2b87b705dcb6..8c9dcf25b6cc 100644
--- a/packages/babel-core/src/config/helpers/config-api.ts
+++ b/packages/babel-core/src/config/helpers/config-api.ts
@@ -24,7 +24,7 @@ type CallerFactory = (
   extractor: (callerMetadata: CallerMetadata | undefined) => unknown,
 ) => SimpleType;
 type TargetsFunction = () => Targets;
-type AssumptionFunction = (name: AssumptionName) => boolean | void;
+type AssumptionFunction = (name: AssumptionName) => boolean | undefined;
 
 export type ConfigAPI = {
   version: string;
diff --git a/packages/babel-helper-create-class-features-plugin/src/decorators.ts b/packages/babel-helper-create-class-features-plugin/src/decorators.ts
index bb80db63a7db..ef34aa56f399 100644
--- a/packages/babel-helper-create-class-features-plugin/src/decorators.ts
+++ b/packages/babel-helper-create-class-features-plugin/src/decorators.ts
@@ -108,9 +108,20 @@ function extractElementDescriptor(
   ].filter(Boolean);
 
   if (t.isClassMethod(node)) {
-    const id = node.computed ? null : node.key;
-    t.toExpression(node);
-    properties.push(prop("value", nameFunction({ node, id, scope }) || node));
+    const id = node.computed
+      ? null
+      : (node.key as
+          | t.Identifier
+          | t.StringLiteral
+          | t.NumericLiteral
+          | t.BigIntLiteral);
+    const transformed = t.toExpression(node);
+    properties.push(
+      prop(
+        "value",
+        nameFunction({ node: transformed, id, scope }) || transformed,
+      ),
+    );
   } else if (t.isClassProperty(node) && node.value) {
     properties.push(
       method("value", template.statements.ast`return ${node.value}`),
diff --git a/packages/babel-helper-create-class-features-plugin/src/fields.ts b/packages/babel-helper-create-class-features-plugin/src/fields.ts
index d938e0a9ce7a..db9c201f614c 100644
--- a/packages/babel-helper-create-class-features-plugin/src/fields.ts
+++ b/packages/babel-helper-create-class-features-plugin/src/fields.ts
@@ -490,7 +490,15 @@ export function transformPrivateNamesUsage(
   ref: t.Identifier,
   path: NodePath<t.Class>,
   privateNamesMap: PrivateNamesMap,
-  { privateFieldsAsProperties, noDocumentAll, innerBinding },
+  {
+    privateFieldsAsProperties,
+    noDocumentAll,
+    innerBinding,
+  }: {
+    privateFieldsAsProperties: boolean;
+    noDocumentAll: boolean;
+    innerBinding: t.Identifier;
+  },
   state: File,
 ) {
   if (!privateNamesMap.size) return;
@@ -539,7 +547,7 @@ function buildPrivateInstanceFieldInitSpec(
   ref: t.Expression,
   prop: NodePath<t.ClassPrivateProperty>,
   privateNamesMap: PrivateNamesMap,
-  state,
+  state: File,
 ) {
   const { id } = privateNamesMap.get(prop.node.key.id.name);
   const value = prop.node.value || prop.scope.buildUndefinedNode();
@@ -646,7 +654,7 @@ function buildPrivateInstanceMethodInitSpec(
   ref: t.Expression,
   prop: NodePath<t.ClassPrivateMethod>,
   privateNamesMap: PrivateNamesMap,
-  state,
+  state: File,
 ) {
   const privateName = privateNamesMap.get(prop.node.key.id.name);
   const { getId, setId, initAdded } = privateName;
@@ -675,7 +683,7 @@ function buildPrivateAccessorInitialization(
   ref: t.Expression,
   prop: NodePath<t.ClassPrivateMethod>,
   privateNamesMap: PrivateNamesMap,
-  state,
+  state: File,
 ) {
   const privateName = privateNamesMap.get(prop.node.key.id.name);
   const { id, getId, setId } = privateName;
@@ -711,7 +719,7 @@ function buildPrivateInstanceMethodInitalization(
   ref: t.Expression,
   prop: NodePath<t.ClassPrivateMethod>,
   privateNamesMap: PrivateNamesMap,
-  state,
+  state: File,
 ) {
   const privateName = privateNamesMap.get(prop.node.key.id.name);
   const { id } = privateName;
@@ -748,7 +756,7 @@ function buildPublicFieldInitLoose(
 function buildPublicFieldInitSpec(
   ref: t.Expression,
   prop: NodePath<t.ClassProperty>,
-  state,
+  state: File,
 ) {
   const { key, computed } = prop.node;
   const value = prop.node.value || prop.scope.buildUndefinedNode();
@@ -767,7 +775,7 @@ function buildPublicFieldInitSpec(
 function buildPrivateStaticMethodInitLoose(
   ref: t.Expression,
   prop: NodePath<t.ClassPrivateMethod>,
-  state,
+  state: File,
   privateNamesMap: PrivateNamesMap,
 ) {
   const privateName = privateNamesMap.get(prop.node.key.id.name);
diff --git a/packages/babel-helper-create-regexp-features-plugin/src/index.ts b/packages/babel-helper-create-regexp-features-plugin/src/index.ts
index 34bd564024ed..060a3638f94d 100644
--- a/packages/babel-helper-create-regexp-features-plugin/src/index.ts
+++ b/packages/babel-helper-create-regexp-features-plugin/src/index.ts
@@ -1,6 +1,7 @@
 import rewritePattern from "regexpu-core";
 import { featuresKey, FEATURES, enableFeature, runtimeKey } from "./features";
 import { generateRegexpuOptions, canSkipRegexpu, transformFlags } from "./util";
+import type { NodePath } from "@babel/traverse";
 
 import { types as t } from "@babel/core";
 import type { PluginObject } from "@babel/core";
@@ -17,12 +18,22 @@ const version = PACKAGE_JSON.version
   .reduce((v, x) => v * 1e5 + +x, 0);
 const versionKey = "@babel/plugin-regexp-features/version";
 
+export interface Options {
+  name: string;
+  feature: keyof typeof FEATURES;
+  options?: {
+    useUnicodeFlag?: boolean;
+    runtime?: boolean;
+  };
+  manipulateOptions?: PluginObject["manipulateOptions"];
+}
+
 export function createRegExpFeaturePlugin({
   name,
   feature,
-  options = {} as any,
-  manipulateOptions = (() => {}) as PluginObject["manipulateOptions"],
-}): PluginObject {
+  options = {},
+  manipulateOptions = () => {},
+}: Options): PluginObject {
   return {
     name,
 
@@ -60,7 +71,7 @@ export function createRegExpFeaturePlugin({
         const regexpuOptions = generateRegexpuOptions(features);
         if (canSkipRegexpu(node, regexpuOptions)) return;
 
-        const namedCaptureGroups = {};
+        const namedCaptureGroups: Record<string, number> = {};
         if (regexpuOptions.namedGroups === "transform") {
           regexpuOptions.onNamedGroup = (name, index) => {
             namedCaptureGroups[name] = index;
@@ -90,7 +101,7 @@ export function createRegExpFeaturePlugin({
   };
 }
 
-function isRegExpTest(path) {
+function isRegExpTest(path: NodePath<t.RegExpLiteral>) {
   return (
     path.parentPath.isMemberExpression({
       object: path.node,
diff --git a/packages/babel-helper-create-regexp-features-plugin/src/util.ts b/packages/babel-helper-create-regexp-features-plugin/src/util.ts
index b8126ad009b3..b4c7e5251dfc 100644
--- a/packages/babel-helper-create-regexp-features-plugin/src/util.ts
+++ b/packages/babel-helper-create-regexp-features-plugin/src/util.ts
@@ -1,14 +1,7 @@
 import type { types as t } from "@babel/core";
 import { FEATURES, hasFeature } from "./features";
 
-type RegexpuOptions = {
-  unicodeFlag: "transform" | false;
-  unicodeSetsFlag: "transform" | "parse" | false;
-  dotAllFlag: "transform" | false;
-  unicodePropertyEscapes: "transform" | false;
-  namedGroups: "transform" | false;
-  onNamedGroup: (name: string, index: number) => void;
-};
+import type { RegexpuOptions } from "regexpu-core";
 
 export function generateRegexpuOptions(toTransform: number): RegexpuOptions {
   type Experimental = 1;
diff --git a/packages/babel-helper-function-name/src/index.ts b/packages/babel-helper-function-name/src/index.ts
index 623b541e4ad1..bd842d3ed636 100644
--- a/packages/babel-helper-function-name/src/index.ts
+++ b/packages/babel-helper-function-name/src/index.ts
@@ -102,7 +102,7 @@ function getNameFromLiteralId(id: t.Literal) {
 
 function wrap(
   state: State,
-  method: t.FunctionExpression | t.ClassExpression,
+  method: t.FunctionExpression | t.Class,
   id: t.Identifier,
   scope: Scope,
 ) {
@@ -148,7 +148,7 @@ function wrap(
 }
 
 function visit(
-  node: t.FunctionExpression | t.ClassExpression,
+  node: t.FunctionExpression | t.Class,
   name: string,
   scope: Scope,
 ) {
@@ -201,21 +201,21 @@ function visit(
  * @param {Boolean} localBinding whether a name could shadow a self-reference (e.g. converting arrow function)
  * @param {Boolean} supportUnicodeId whether a target support unicodeId or not
  */
-export default function (
+export default function <N extends t.FunctionExpression | t.Class>(
   {
     node,
     parent,
     scope,
     id,
   }: {
-    node: t.FunctionExpression | t.ClassExpression;
+    node: N;
     parent?: t.Node;
     scope: Scope;
     id?: any;
   },
   localBinding = false,
   supportUnicodeId = false,
-) {
+): t.CallExpression | N {
   // has an `id` so we don't need to infer one
   if (node.id) return;
 
diff --git a/packages/babel-plugin-transform-flow-comments/src/index.ts b/packages/babel-plugin-transform-flow-comments/src/index.ts
index 666e2c8f0e11..db0573c27ff2 100644
--- a/packages/babel-plugin-transform-flow-comments/src/index.ts
+++ b/packages/babel-plugin-transform-flow-comments/src/index.ts
@@ -7,7 +7,7 @@ import type { NodePath } from "@babel/traverse";
 export default declare(api => {
   api.assertVersion(7);
 
-  function commentFromString(comment) {
+  function commentFromString(comment: string | t.Comment): t.Comment {
     return typeof comment === "string"
       ? { type: "CommentBlock", value: comment }
       : comment;
@@ -21,12 +21,12 @@ export default declare(api => {
     comments = generateComment(ofPath, optional),
     keepType = false,
   }: {
-    ofPath?;
-    toPath?;
-    where?: string;
-    optional?;
-    comments?;
-    keepType?;
+    ofPath?: NodePath;
+    toPath?: NodePath;
+    where?: t.CommentTypeShorthand;
+    optional?: boolean;
+    comments?: string | t.Comment | (string | t.Comment)[];
+    keepType?: boolean;
   }) {
     if (!toPath?.node) {
       toPath = ofPath.getPrevSibling();
@@ -43,7 +43,7 @@ export default declare(api => {
     if (!Array.isArray(comments)) {
       comments = [comments];
     }
-    comments = comments.map(commentFromString);
+    const newComments = comments.map(commentFromString);
     if (!keepType && ofPath?.node) {
       // Removes the node at `ofPath` while conserving the comments attached
       // to it.
@@ -58,24 +58,28 @@ export default declare(api => {
       if (isSingleChild && leading) {
         parent.addComments("inner", leading);
       }
-      toPath.addComments(where, comments);
+      toPath.addComments(where, newComments);
       ofPath.remove();
       if (isSingleChild && trailing) {
         parent.addComments("inner", trailing);
       }
     } else {
-      toPath.addComments(where, comments);
+      toPath.addComments(where, newComments);
     }
   }
 
-  function wrapInFlowComment(path) {
+  function wrapInFlowComment(path: NodePath) {
     attachComment({
       ofPath: path,
-      comments: generateComment(path, path.parent.optional),
+      comments: generateComment(
+        path,
+        // @ts-ignore
+        path.parent.optional,
+      ),
     });
   }
 
-  function generateComment(path, optional?) {
+  function generateComment(path: NodePath, optional?: boolean | void) {
     let comment = path
       .getSource()
       .replace(/\*-\//g, "*-ESCAPED/")
@@ -85,7 +89,7 @@ export default declare(api => {
     return comment;
   }
 
-  function isTypeImport(importKind) {
+  function isTypeImport(importKind: "type" | "typeof" | "value") {
     return importKind === "type" || importKind === "typeof";
   }
 
@@ -236,7 +240,11 @@ export default declare(api => {
         }
       },
 
-      Flow(path) {
+      Flow(
+        path: NodePath<
+          t.Flow | t.ImportDeclaration | t.ExportDeclaration | t.ImportSpecifier
+        >,
+      ) {
         wrapInFlowComment(path);
       },
 
diff --git a/packages/babel-plugin-transform-flow-strip-types/src/index.ts b/packages/babel-plugin-transform-flow-strip-types/src/index.ts
index 8030a99f9c77..aaffbfc3d6cd 100644
--- a/packages/babel-plugin-transform-flow-strip-types/src/index.ts
+++ b/packages/babel-plugin-transform-flow-strip-types/src/index.ts
@@ -1,6 +1,7 @@
 import { declare } from "@babel/helper-plugin-utils";
 import syntaxFlow from "@babel/plugin-syntax-flow";
 import { types as t } from "@babel/core";
+import type { NodePath } from "@babel/traverse";
 
 export interface Options {
   requireDirective?: boolean;
@@ -75,7 +76,11 @@ export default declare((api, opts: Options) => {
         }
       },
 
-      Flow(path) {
+      Flow(
+        path: NodePath<
+          t.Flow | t.ImportDeclaration | t.ExportDeclaration | t.ImportSpecifier
+        >,
+      ) {
         if (skipStrip) {
           throw path.buildCodeFrameError(
             "A @flow directive is required when using Flow annotations with " +
diff --git a/packages/babel-plugin-transform-for-of/src/index.ts b/packages/babel-plugin-transform-for-of/src/index.ts
index b574640d7c5a..edce0e1baca9 100644
--- a/packages/babel-plugin-transform-for-of/src/index.ts
+++ b/packages/babel-plugin-transform-for-of/src/index.ts
@@ -154,15 +154,17 @@ export default declare((api, options: Options) => {
     ? {
         build: buildForOfNoIteratorClosing,
         helper: "createForOfIteratorHelperLoose",
-        getContainer: nodes => nodes,
+        getContainer: (nodes: t.Statement[]): [t.ForStatement] =>
+          nodes as [t.ForStatement],
       }
     : {
         build: buildForOf,
         helper: "createForOfIteratorHelper",
-        getContainer: nodes => nodes[1].block.body,
+        getContainer: (nodes: t.Statement[]): [t.ForStatement] =>
+          (nodes[1] as t.TryStatement).block.body as [t.ForStatement],
       };
 
-  function _ForOfStatementArray(path) {
+  function _ForOfStatementArray(path: NodePath<t.ForOfStatement>) {
     const { node, scope } = path;
 
     const right = scope.generateUidIdentifierBasedOnNode(node.right, "arr");
@@ -257,6 +259,7 @@ export default declare((api, options: Options) => {
         t.inherits(container[0].body, node.body);
 
         if (t.isLabeledStatement(parent)) {
+          // @ts-expect-error replacing node types
           container[0] = t.labeledStatement(parent.label, container[0]);
 
           path.parentPath.replaceWithMultiple(nodes);
diff --git a/packages/babel-plugin-transform-for-of/src/no-helper-implementation.ts b/packages/babel-plugin-transform-for-of/src/no-helper-implementation.ts
index d84143b6e338..fbf4afc5e8ae 100644
--- a/packages/babel-plugin-transform-for-of/src/no-helper-implementation.ts
+++ b/packages/babel-plugin-transform-for-of/src/no-helper-implementation.ts
@@ -1,10 +1,15 @@
-import { template, types as t } from "@babel/core";
+import { type PluginPass, template, types as t } from "@babel/core";
+import type { NodePath } from "@babel/traverse";
 
 // This is the legacy implementation, which inlines all the code.
 // It must be kept for compatibility reasons.
 // TODO (Babel 8): Remove this code.
 
-export default function transformWithoutHelper(loose, path, state) {
+export default function transformWithoutHelper(
+  loose: boolean | void,
+  path: NodePath<t.ForOfStatement>,
+  state: PluginPass,
+) {
   const pushComputedProps = loose
     ? pushComputedPropsLoose
     : pushComputedPropsSpec;
@@ -13,7 +18,7 @@ export default function transformWithoutHelper(loose, path, state) {
   const build = pushComputedProps(path, state);
   const declar = build.declar;
   const loop = build.loop;
-  const block = loop.body;
+  const block = loop.body as t.BlockStatement;
 
   // ensure that it's a block so we can take all its statements
   path.ensureBlock();
@@ -24,7 +29,7 @@ export default function transformWithoutHelper(loose, path, state) {
   }
 
   // push the rest of the original loop body onto our new body
-  block.body.push(...node.body.body);
+  block.body.push(...(node.body as t.BlockStatement).body);
 
   t.inherits(loop, node);
   t.inherits(loop.body, node.body);
@@ -37,7 +42,7 @@ export default function transformWithoutHelper(loose, path, state) {
   }
 }
 
-const buildForOfLoose = template(`
+const buildForOfLoose = template.statement(`
   for (var LOOP_OBJECT = OBJECT,
           IS_ARRAY = Array.isArray(LOOP_OBJECT),
           INDEX = 0,
@@ -54,7 +59,7 @@ const buildForOfLoose = template(`
   }
 `);
 
-const buildForOf = template(`
+const buildForOf = template.statements(`
   var ITERATOR_COMPLETION = true;
   var ITERATOR_HAD_ERROR_KEY = false;
   var ITERATOR_ERROR_KEY = undefined;
@@ -80,7 +85,10 @@ const buildForOf = template(`
   }
 `);
 
-function pushComputedPropsLoose(path, file) {
+function pushComputedPropsLoose(
+  path: NodePath<t.ForOfStatement>,
+  state: PluginPass,
+) {
   const { node, scope, parent } = path;
   const { left } = node;
   let declar, id, intermediate;
@@ -99,7 +107,7 @@ function pushComputedPropsLoose(path, file) {
       t.variableDeclarator(t.identifier(id.name)),
     ]);
   } else {
-    throw file.buildCodeFrameError(
+    throw state.buildCodeFrameError(
       left,
       `Unknown node type ${left.type} in ForStatement`,
     );
@@ -115,7 +123,7 @@ function pushComputedPropsLoose(path, file) {
     INDEX: scope.generateUidIdentifier("i"),
     ID: id,
     INTERMEDIATE: intermediate,
-  }) as t.Statement;
+  }) as t.ForStatement;
 
   //
   const isLabeledParent = t.isLabeledStatement(parent);
@@ -133,7 +141,10 @@ function pushComputedPropsLoose(path, file) {
   };
 }
 
-function pushComputedPropsSpec(path, file) {
+function pushComputedPropsSpec(
+  path: NodePath<t.ForOfStatement>,
+  state: PluginPass,
+) {
   const { node, scope, parent } = path;
   const left = node.left;
   let declar;
@@ -155,7 +166,7 @@ function pushComputedPropsSpec(path, file) {
       t.variableDeclarator(left.declarations[0].id, stepValue),
     ]);
   } else {
-    throw file.buildCodeFrameError(
+    throw state.buildCodeFrameError(
       left,
       `Unknown node type ${left.type} in ForStatement`,
     );
@@ -174,8 +185,8 @@ function pushComputedPropsSpec(path, file) {
 
   const isLabeledParent = t.isLabeledStatement(parent);
 
-  const tryBody = template[3].block.body;
-  const loop = tryBody[0];
+  const tryBody = (template[3] as t.TryStatement).block.body;
+  const loop = tryBody[0] as t.ForStatement;
 
   if (isLabeledParent) {
     tryBody[0] = t.labeledStatement(parent.label, loop);
diff --git a/packages/babel-plugin-transform-function-name/src/index.ts b/packages/babel-plugin-transform-function-name/src/index.ts
index 7bdae7fca350..35600a9215fc 100644
--- a/packages/babel-plugin-transform-function-name/src/index.ts
+++ b/packages/babel-plugin-transform-function-name/src/index.ts
@@ -25,7 +25,12 @@ export default declare(api => {
       ObjectProperty(path) {
         const value = path.get("value");
         if (value.isFunction()) {
-          const newNode = nameFunction(value, false, supportUnicodeId);
+          const newNode = nameFunction(
+            // @ts-ignore Fixme: should check ArrowFunctionExpression
+            value,
+            false,
+            supportUnicodeId,
+          );
           if (newNode) value.replaceWith(newNode);
         }
       },
diff --git a/packages/babel-plugin-transform-object-super/src/index.ts b/packages/babel-plugin-transform-object-super/src/index.ts
index b375f575f92f..86df844f2cf1 100644
--- a/packages/babel-plugin-transform-object-super/src/index.ts
+++ b/packages/babel-plugin-transform-object-super/src/index.ts
@@ -1,8 +1,13 @@
 import { declare } from "@babel/helper-plugin-utils";
 import ReplaceSupers from "@babel/helper-replace-supers";
-import { types as t } from "@babel/core";
-
-function replacePropertySuper(path, getObjectRef, file) {
+import { types as t, type File } from "@babel/core";
+import type { NodePath } from "@babel/traverse";
+
+function replacePropertySuper(
+  path: NodePath<t.ObjectMethod>,
+  getObjectRef: () => t.Identifier,
+  file: File,
+) {
   // @ts-expect-error todo(flow->ts):
   const replaceSupers = new ReplaceSupers({
     getObjectRef: getObjectRef,
@@ -21,14 +26,14 @@ export default declare(api => {
 
     visitor: {
       ObjectExpression(path, state) {
-        let objectRef;
+        let objectRef: t.Identifier;
         const getObjectRef = () =>
           (objectRef = objectRef || path.scope.generateUidIdentifier("obj"));
 
         path.get("properties").forEach(propPath => {
           if (!propPath.isMethod()) return;
 
-          replacePropertySuper(propPath, getObjectRef, state);
+          replacePropertySuper(propPath, getObjectRef, state.file);
         });
 
         if (objectRef) {
diff --git a/packages/babel-plugin-transform-proto-to-assign/src/index.ts b/packages/babel-plugin-transform-proto-to-assign/src/index.ts
index bd29c5933ff2..1bd61aeeb755 100644
--- a/packages/babel-plugin-transform-proto-to-assign/src/index.ts
+++ b/packages/babel-plugin-transform-proto-to-assign/src/index.ts
@@ -1,22 +1,35 @@
 import { declare } from "@babel/helper-plugin-utils";
-import { types as t } from "@babel/core";
+import { types as t, type File } from "@babel/core";
 
 export default declare(api => {
   api.assertVersion(7);
 
-  function isProtoKey(node) {
-    return t.isLiteral(t.toComputedKey(node, node.key), { value: "__proto__" });
+  function isProtoKey(node: t.ObjectExpression["properties"][number]) {
+    return (
+      !t.isSpreadElement(node) &&
+      t.isStringLiteral(t.toComputedKey(node, node.key), {
+        value: "__proto__",
+      })
+    );
   }
 
-  function isProtoAssignmentExpression(node): node is t.MemberExpression {
+  function isProtoAssignmentExpression(
+    node: t.Node,
+  ): node is t.MemberExpression {
     const left = node;
     return (
       t.isMemberExpression(left) &&
-      t.isLiteral(t.toComputedKey(left, left.property), { value: "__proto__" })
+      t.isStringLiteral(t.toComputedKey(left, left.property), {
+        value: "__proto__",
+      })
     );
   }
 
-  function buildDefaultsCallExpression(expr, ref, file) {
+  function buildDefaultsCallExpression(
+    expr: t.AssignmentExpression,
+    ref: t.MemberExpression["object"],
+    file: File,
+  ) {
     return t.expressionStatement(
       t.callExpression(file.addHelper("defaults"), [ref, expr.right]),
     );
@@ -26,7 +39,7 @@ export default declare(api => {
     name: "transform-proto-to-assign",
 
     visitor: {
-      AssignmentExpression(path, file) {
+      AssignmentExpression(path, { file }) {
         if (!isProtoAssignmentExpression(path.node.left)) return;
 
         const nodes = [];
@@ -50,7 +63,7 @@ export default declare(api => {
         path.replaceWithMultiple(nodes);
       },
 
-      ExpressionStatement(path, file) {
+      ExpressionStatement(path, { file }) {
         const expr = path.node.expression;
         if (!t.isAssignmentExpression(expr, { operator: "=" })) return;
 
@@ -61,7 +74,7 @@ export default declare(api => {
         }
       },
 
-      ObjectExpression(path, file) {
+      ObjectExpression(path, { file }) {
         let proto;
         const { node } = path;
         const { properties } = node;
diff --git a/packages/babel-plugin-transform-react-constant-elements/src/index.ts b/packages/babel-plugin-transform-react-constant-elements/src/index.ts
index c759d49e6533..bc1a89f3fe0b 100644
--- a/packages/babel-plugin-transform-react-constant-elements/src/index.ts
+++ b/packages/babel-plugin-transform-react-constant-elements/src/index.ts
@@ -29,7 +29,7 @@ export default declare((api, options: Options) => {
   // Element -> Target scope
   const HOISTED = new WeakMap();
 
-  function declares(node: t.Identifier | t.JSXIdentifier, scope) {
+  function declares(node: t.Identifier | t.JSXIdentifier, scope: Scope) {
     if (
       t.isJSXIdentifier(node, { name: "this" }) ||
       t.isJSXIdentifier(node, { name: "arguments" }) ||
@@ -43,11 +43,11 @@ export default declare((api, options: Options) => {
     return scope.hasOwnBinding(node.name);
   }
 
-  function isHoistingScope({ path }) {
+  function isHoistingScope({ path }: Scope) {
     return path.isFunctionParent() || path.isLoop() || path.isProgram();
   }
 
-  function getHoistingScope(scope) {
+  function getHoistingScope(scope: Scope) {
     while (!isHoistingScope(scope)) scope = scope.parent;
     return scope;
   }
diff --git a/packages/babel-plugin-transform-unicode-escapes/src/index.ts b/packages/babel-plugin-transform-unicode-escapes/src/index.ts
index f21e9cfdaf5c..da962b899f38 100644
--- a/packages/babel-plugin-transform-unicode-escapes/src/index.ts
+++ b/packages/babel-plugin-transform-unicode-escapes/src/index.ts
@@ -1,5 +1,6 @@
 import { declare } from "@babel/helper-plugin-utils";
 import { types as t } from "@babel/core";
+import type { NodePath } from "@babel/traverse";
 
 export default declare(api => {
   api.assertVersion(7);
@@ -7,7 +8,7 @@ export default declare(api => {
   const surrogate = /[\ud800-\udfff]/g;
   const unicodeEscape = /(\\+)u\{([0-9a-fA-F]+)\}/g;
 
-  function escape(code) {
+  function escape(code: number) {
     let str = code.toString(16);
     // Sigh, node 6 doesn't have padStart
     // TODO: Remove in Babel 8, when we drop node 6.
@@ -15,7 +16,7 @@ export default declare(api => {
     return "\\u" + str;
   }
 
-  function replacer(match, backslashes, code) {
+  function replacer(match: string, backslashes: string[], code: string) {
     if (backslashes.length % 2 === 0) {
       return match;
     }
@@ -26,11 +27,11 @@ export default declare(api => {
     return char.length === 1 ? escaped : escaped + escape(char.charCodeAt(1));
   }
 
-  function replaceUnicodeEscapes(str) {
+  function replaceUnicodeEscapes(str: string) {
     return str.replace(unicodeEscape, replacer);
   }
 
-  function getUnicodeEscape(str) {
+  function getUnicodeEscape(str: string) {
     let match;
     while ((match = unicodeEscape.exec(str))) {
       if (match[1].length % 2 === 0) continue;
@@ -88,11 +89,13 @@ export default declare(api => {
         );
       },
 
-      "StringLiteral|DirectiveLiteral"(path) {
+      "StringLiteral|DirectiveLiteral"(
+        path: NodePath<t.StringLiteral | t.DirectiveLiteral>,
+      ) {
         const { node } = path;
         const { extra } = node;
 
-        if (extra?.raw) extra.raw = replaceUnicodeEscapes(extra.raw);
+        if (extra?.raw) extra.raw = replaceUnicodeEscapes(extra.raw as string);
       },
 
       TemplateElement(path) {
diff --git a/packages/babel-traverse/src/path/replacement.ts b/packages/babel-traverse/src/path/replacement.ts
index bf7f388d2d9c..25dc6ad86f09 100644
--- a/packages/babel-traverse/src/path/replacement.ts
+++ b/packages/babel-traverse/src/path/replacement.ts
@@ -40,7 +40,7 @@ import hoistVariables from "@babel/helper-hoist-variables";
 
 export function replaceWithMultiple(
   this: NodePath,
-  nodes: t.Node[],
+  nodes: t.Node | t.Node[],
 ): NodePath[] {
   this.resync();
 
diff --git a/packages/babel-types/scripts/generators/ast-types.js b/packages/babel-types/scripts/generators/ast-types.js
index 49b67bba38a8..b0c14ff3410e 100644
--- a/packages/babel-types/scripts/generators/ast-types.js
+++ b/packages/babel-types/scripts/generators/ast-types.js
@@ -7,9 +7,9 @@ export default function generateAstTypes() {
 
 interface BaseComment {
   value: string;
-  start: number;
-  end: number;
-  loc: SourceLocation;
+  start?: number;
+  end?: number;
+  loc?: SourceLocation;
   type: "CommentBlock" | "CommentLine";
 }
 
diff --git a/packages/babel-types/src/ast-types/generated/index.ts b/packages/babel-types/src/ast-types/generated/index.ts
index a13ee342a030..a230acd945ec 100644
--- a/packages/babel-types/src/ast-types/generated/index.ts
+++ b/packages/babel-types/src/ast-types/generated/index.ts
@@ -3,9 +3,9 @@
 
 interface BaseComment {
   value: string;
-  start: number;
-  end: number;
-  loc: SourceLocation;
+  start?: number;
+  end?: number;
+  loc?: SourceLocation;
   type: "CommentBlock" | "CommentLine";
 }
 
diff --git a/scripts/generators/tsconfig.js b/scripts/generators/tsconfig.js
index 4afca0f767c4..37f2156e421b 100644
--- a/scripts/generators/tsconfig.js
+++ b/scripts/generators/tsconfig.js
@@ -117,6 +117,7 @@ fs.writeFileSync(
               ["./lib/babel-plugin-dynamic-import-node.d.ts"],
             ],
             ["globals", ["./node_modules/globals-BABEL_8_BREAKING-true"]],
+            ["regexpu-core", ["./lib/regexpu-core.d.ts"]],
           ]),
         },
       },
diff --git a/tsconfig.json b/tsconfig.json
index 86f6aec802c9..8fce7ecacb84 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -701,6 +701,9 @@
       ],
       "globals": [
         "./node_modules/globals-BABEL_8_BREAKING-true"
+      ],
+      "regexpu-core": [
+        "./lib/regexpu-core.d.ts"
       ]
     }
   }