refactor: fix hidden eslint errors (#49365)

* refactor: explicit types for validate

* refactor: explicit return types for ui-components

* refactor: use exec instead of match

* refactor: add lots more boundary types

* refactor: more eslint warnings

* refactor: more explicit exports

* refactor: more explicit types

* refactor: even more explicit types

* fix: relax type contrainsts for superblock-order

* refactor: final boundaries

* refactor: avoid using 'object' type

* fix: use named import for captureException

This uses TypeScript (which works) instead of import/namespace
(which doesn't) to check if captureException exists in sentry/gatsby
(it does)

client/i18n/schema-validation.ts

@@ -215,7 +215,7 @@ const schemaValidation = (
   if (
     fileName === 'motivation' &&
     !(fileJson.motivationalQuotes as MotivationalQuotes).every(
-      (object: object) =>
+      object =>
         Object.prototype.hasOwnProperty.call(object, 'quote') &&
         Object.prototype.hasOwnProperty.call(object, 'author')
     )

client/src/components/SolutionViewer/SolutionViewer.tsx

@@ -9,7 +9,7 @@ type Props = {
 };
 type Solution = Pick<ChallengeFile, 'ext' | 'contents' | 'fileKey'>;
 
-function SolutionViewer({ challengeFiles, solution }: Props) {
+function SolutionViewer({ challengeFiles, solution }: Props): JSX.Element {
   const isLegacy = !challengeFiles || !challengeFiles.length;
   const solutions = isLegacy
     ? [

client/src/components/helpers/full-width-row.tsx

@@ -6,15 +6,16 @@ interface FullWidthRowProps {
   className?: string;
 }
 
-const FullWidthRow = ({ children, className }: FullWidthRowProps) => {
-  return (
-    <Row className={className}>
-      <Col sm={8} smOffset={2} xs={12}>
-        {children}
-      </Col>
-    </Row>
-  );
-};
+const FullWidthRow = ({
+  children,
+  className
+}: FullWidthRowProps): JSX.Element => (
+  <Row className={className}>
+    <Col sm={8} smOffset={2} xs={12}>
+      {children}
+    </Col>
+  </Row>
+);
 
 FullWidthRow.displayName = 'FullWidthRow';
 

client/src/components/seo/index.tsx

@@ -17,10 +17,23 @@ interface SiteData {
   };
 }
 
+interface Item {
+  '@type': 'Course';
+  url: string;
+  name: string;
+  description?: string;
+  provider: {
+    '@type': 'Organization';
+    name: string;
+    sameAs: string;
+    nonprofitStatus: string;
+  };
+}
+
 interface ListItem {
   '@type': 'ListItem';
   position: number;
-  item: object;
+  item: Item;
 }
 
 interface StructuredData {

client/src/components/solution-display-widget/index.tsx

@@ -22,7 +22,7 @@ export function SolutionDisplayWidget({
   showUserCode,
   showProjectPreview,
   displayContext
-}: Props) {
+}: Props): JSX.Element | null {
   const { id, solution, githubLink } = completedChallenge;
   const { t } = useTranslation();
   const viewText = t('buttons.view');

client/src/templates/Challenges/classic/mobile-layout.tsx

@@ -39,17 +39,17 @@ class MobileLayout extends Component<MobileLayoutProps, MobileLayoutState> {
     currentTab: this.props.hasEditableBoundaries ? Tab.Editor : Tab.Instructions
   };
 
-  switchTab = (tab: Tab) => {
+  switchTab = (tab: Tab): void => {
     this.setState({
       currentTab: tab
     });
   };
 
-  handleKeyDown = () => this.props.updateUsingKeyboardInTablist(true);
+  handleKeyDown = (): void => this.props.updateUsingKeyboardInTablist(true);
 
-  handleClick = () => this.props.updateUsingKeyboardInTablist(false);
+  handleClick = (): void => this.props.updateUsingKeyboardInTablist(false);
 
-  render() {
+  render(): JSX.Element {
     const { currentTab } = this.state;
     const {
       hasEditableBoundaries,

client/src/templates/Challenges/rechallenge/builders.ts

@@ -10,7 +10,7 @@ export function concatHtml({
   required = [],
   template,
   contents
-}: ConcatHTMLOptions) {
+}: ConcatHTMLOptions): string {
   const embedSource = template
     ? _template(template)
     : ({ source }: { source: ConcatHTMLOptions['contents'] }) => source;

client/src/templates/Challenges/utils/build.ts

@@ -107,11 +107,13 @@ const buildFunctions = {
   [challengeTypes.multifileCertProject]: buildDOMChallenge
 };
 
-export function canBuildChallenge(challengeData: BuildChallengeData) {
+export function canBuildChallenge(challengeData: BuildChallengeData): boolean {
   const { challengeType } = challengeData;
   return Object.prototype.hasOwnProperty.call(buildFunctions, challengeType);
 }
 
+// TODO: Figure out and (hopefully) simplify the return type.
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export async function buildChallenge(
   challengeData: BuildChallengeData,
   options: BuildOptions
@@ -131,6 +133,8 @@ const testRunners = {
   [challengeTypes.pythonProject]: getDOMTestRunner,
   [challengeTypes.multifileCertProject]: getDOMTestRunner
 };
+// TODO: Figure out and (hopefully) simplify the return type.
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export function getTestRunner(
   buildData: BuildChallengeData,
   runnerConfig: TestRunnerConfig,
@@ -185,10 +189,16 @@ async function getDOMTestRunner(
     runTestInTestFrame(document, testString, testTimeout);
 }
 
+type BuildResult = {
+  challengeType: number;
+  build: string;
+  sources: Source | undefined;
+};
+
 export function buildDOMChallenge(
   { challengeFiles, required = [], template = '' }: BuildChallengeData,
   { usesTestRunner } = { usesTestRunner: false }
-) {
+): Promise<BuildResult> | undefined {
   const finalRequires = [...required];
   if (usesTestRunner) finalRequires.push(...frameRunner);
 
@@ -225,7 +235,7 @@ export function buildDOMChallenge(
 export function buildJSChallenge(
   { challengeFiles }: { challengeFiles: ChallengeFiles },
   options: BuildOptions
-) {
+): Promise<BuildResult> | undefined {
   const pipeLine = composeFunctions(...getTransformers(options));
 
   const finalFiles = challengeFiles?.map(pipeLine);
@@ -262,7 +272,7 @@ export function updatePreview(
   buildData: BuildChallengeData,
   document: Document,
   proxyLogger: ProxyLogger
-) {
+): void {
   if (
     buildData.challengeType === challengeTypes.html ||
     buildData.challengeType === challengeTypes.multifileCertProject
@@ -293,7 +303,7 @@ function getDocumentTitle(buildData: BuildChallengeData) {
 export function updateProjectPreview(
   buildData: BuildChallengeData,
   document: Document
-) {
+): void {
   if (
     buildData.challengeType === challengeTypes.html ||
     buildData.challengeType === challengeTypes.multifileCertProject
@@ -309,7 +319,7 @@ export function updateProjectPreview(
   }
 }
 
-export function challengeHasPreview({ challengeType }: ChallengeMeta) {
+export function challengeHasPreview({ challengeType }: ChallengeMeta): boolean {
   return (
     challengeType === challengeTypes.html ||
     challengeType === challengeTypes.modern ||
@@ -317,13 +327,15 @@ export function challengeHasPreview({ challengeType }: ChallengeMeta) {
   );
 }
 
-export function isJavaScriptChallenge({ challengeType }: ChallengeMeta) {
+export function isJavaScriptChallenge({
+  challengeType
+}: ChallengeMeta): boolean {
   return (
     challengeType === challengeTypes.js ||
     challengeType === challengeTypes.jsProject
   );
 }
 
-export function isLoopProtected(challengeMeta: ChallengeMeta) {
+export function isLoopProtected(challengeMeta: ChallengeMeta): boolean {
   return challengeMeta.superBlock !== 'coding-interview-prep';
 }

client/src/templates/Challenges/utils/frame.ts

@@ -132,11 +132,15 @@ const createHeader = (id = mainPreviewId) => `
   </script>
 `;
 
+type TestResult =
+  | { pass: boolean }
+  | { err: { message: string; stack?: string } };
+
 export const runTestInTestFrame = async function (
   document: Document,
   test: string,
   timeout: number
-) {
+): Promise<TestResult | undefined> {
   const { contentDocument: frame } = document.getElementById(
     testId
   ) as HTMLIFrameElement;
@@ -309,7 +313,7 @@ export const createMainPreviewFramer = (
   document: Document,
   proxyLogger: ProxyLogger,
   frameTitle: string
-) =>
+): ((args: Context) => void) =>
   createFramer(
     document,
     mainPreviewId,
@@ -322,7 +326,7 @@ export const createMainPreviewFramer = (
 export const createProjectPreviewFramer = (
   document: Document,
   frameTitle: string
-) =>
+): ((args: Context) => void) =>
   createFramer(
     document,
     projectPreviewId,
@@ -336,7 +340,8 @@ export const createTestFramer = (
   document: Document,
   proxyLogger: ProxyLogger,
   frameReady: () => void
-) => createFramer(document, testId, initTestFrame, proxyLogger, frameReady);
+): ((args: Context) => void) =>
+  createFramer(document, testId, initTestFrame, proxyLogger, frameReady);
 
 const createFramer = (
   document: Document,

client/src/templates/Challenges/utils/index.ts

@@ -35,7 +35,7 @@ export function transformEditorLink(url: string): string {
 
 export function enhancePrismAccessibility(
   prismEnv: Prism.hooks.ElementHighlightedEnvironment
-) {
+): void {
   const langs: { [key: string]: string } = {
     js: 'JavaScript',
     javascript: 'JavaScript',

client/src/utils/ajax.ts

@@ -136,6 +136,8 @@ function parseApiResponseToClientUser(data: ApiUser): UserResponse {
   };
 }
 
+// TODO: this at least needs a few aliases so it's human readable
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export function mapFilesToChallengeFiles<File, Rest>(
   fileContainer: ({ files: (File & { key: string })[] } & Rest)[] = []
 ) {

client/src/utils/challenge-request-helpers.ts

@@ -13,11 +13,25 @@ interface StandardizeRequestBodyArgs {
   challengeType: number;
 }
 
+interface File {
+  contents: string;
+  ext: string;
+  history: string[];
+  key: string;
+  name: string;
+}
+
+interface Body {
+  id: string;
+  files?: File[];
+  challengeType: number;
+}
+
 export function standardizeRequestBody({
   id,
   challengeFiles = [],
   challengeType
-}: StandardizeRequestBodyArgs) {
+}: StandardizeRequestBodyArgs): Body {
   return {
     id,
     files: challengeFiles?.map(({ fileKey, contents, ext, name, history }) => {
@@ -33,12 +47,12 @@ export function standardizeRequestBody({
   };
 }
 
-export function getStringSizeInBytes(str = '') {
+export function getStringSizeInBytes(str = ''): number {
   const stringSizeInBytes = new Blob([JSON.stringify(str)]).size;
 
   return stringSizeInBytes;
 }
 
-export function bodySizeFits(bodySizeInBytes: number) {
+export function bodySizeFits(bodySizeInBytes: number): boolean {
   return bodySizeInBytes <= MAX_BODY_SIZE;
 }

client/src/utils/report-error.ts

@@ -1,4 +1,4 @@
-import * as Sentry from '@sentry/gatsby';
+import { captureException } from '@sentry/gatsby';
 import envData from '../../../config/env.json';
 
 const { sentryClientDSN } = envData;
@@ -11,5 +11,5 @@ export function reportClientSideError(
 ): string | void {
   return sentryClientDSN === null
     ? console.error(`Client: ${message}`, e)
-    : Sentry.captureException(e);
+    : captureException(e);
 }

client/src/utils/solution-display-type.ts

@@ -2,12 +2,20 @@ import type { CompletedChallenge } from '../redux/prop-types';
 import { challengeTypes } from '../../utils/challenge-types';
 import { maybeUrlRE } from '.';
 
+// eslint-disable-next-line @typescript-eslint/naming-convention
+type DisplayType =
+  | 'none'
+  | 'showMultifileProjectSolution'
+  | 'showUserCode'
+  | 'showProjectAndGithubLinks'
+  | 'showProjectLink';
+
 export const getSolutionDisplayType = ({
   solution,
   githubLink,
   challengeFiles,
   challengeType
-}: CompletedChallenge) => {
+}: CompletedChallenge): DisplayType => {
   if (challengeFiles?.length)
     return challengeType === challengeTypes.multifileCertProject
       ? 'showMultifileProjectSolution'

client/src/utils/superblock-map-titles.ts

@@ -14,7 +14,7 @@ const superBlocksWithoutLastWord = [
   SuperBlocks.TheOdinProject
 ];
 
-export function getSuperBlockTitleForMap(superBlock: SuperBlocks) {
+export function getSuperBlockTitleForMap(superBlock: SuperBlocks): string {
   const i18nSuperBlock = i18next.t(`intro:${superBlock}.title`);
 
   return superBlocksWithoutLastWord.includes(superBlock)

config/donation-settings.ts

@@ -80,8 +80,22 @@ export const paypalConfigTypes = {
   }
 };
 
+type DonationAmount = 500 | 1000 | 2000 | 3000 | 4000 | 5000;
+
+interface OneTimeConfig {
+  amount: DonationAmount;
+  duration: 'one-time';
+  planId: null;
+}
+
+interface SubscriptionConfig {
+  amount: DonationAmount;
+  duration: 'month';
+  planId: string;
+}
+
 export const paypalConfigurator = (
-  donationAmount: 500 | 1000 | 2000 | 3000 | 4000 | 5000,
+  donationAmount: DonationAmount,
   donationDuration: 'one-time' | 'month',
   paypalConfig: {
     month: {
@@ -93,7 +107,7 @@ export const paypalConfigurator = (
       5000: { planId: string };
     };
   }
-) => {
+): OneTimeConfig | SubscriptionConfig => {
   if (donationDuration === 'one-time') {
     return { amount: donationAmount, duration: donationDuration, planId: null };
   }

config/i18n.ts

@@ -111,7 +111,7 @@ export const rtlLangs = ['arabic'];
 // locale is sourced from a JSON file, so we use getLangCode to
 // find the associated enum values
 
-export function getLangCode(locale: PropertyKey) {
+export function getLangCode(locale: PropertyKey): string {
   if (isPropertyOf(LangCodes, locale)) return LangCodes[locale];
   throw new Error(`${String(locale)} is not a valid locale`);
 }

config/superblock-order.ts

@@ -576,11 +576,17 @@ function shouldShowSuperblocks({
   return true;
 }
 
+type Config = {
+  language: string;
+  showNewCurriculum?: string;
+  showUpcomingChanges?: string;
+};
+
 export function getLearnSuperBlocks({
   language = 'english',
   showNewCurriculum = 'false',
   showUpcomingChanges = 'false'
-}) {
+}: Config): SuperBlocks[] {
   const learnSuperBlocks: SuperBlocks[] = [];
 
   Object.values(TranslationStates).forEach(translationState => {
@@ -608,7 +614,7 @@ export function getAuditedSuperBlocks({
   language = 'english',
   showNewCurriculum = 'false',
   showUpcomingChanges = 'false'
-}) {
+}: Config): SuperBlocks[] {
   const auditedSuperBlocks: SuperBlocks[] = [];
 
   Object.values(SuperBlockStates).forEach(superBlockState => {
@@ -634,7 +640,7 @@ export function getNotAuditedSuperBlocks({
   language = 'english',
   showNewCurriculum = 'false',
   showUpcomingChanges = 'false'
-}) {
+}: Config): SuperBlocks[] {
   const notAuditedSuperBlocks: SuperBlocks[] = [];
 
   Object.values(SuperBlockStates).forEach(superBlockState => {

tools/challenge-editor/api/routes/block-route.ts

@@ -1,7 +1,10 @@
 import { Request, Response } from 'express';
 import { getSteps } from '../utils/get-steps';
 
-export const blockRoute = async (req: Request, res: Response) => {
+export const blockRoute = async (
+  req: Request,
+  res: Response
+): Promise<void> => {
   const { superblock, block } = req.params;
 
   const steps = await getSteps(superblock, block);

tools/challenge-editor/api/routes/index-route.ts

@@ -1,6 +1,6 @@
 import { Request, Response } from 'express';
 import { superBlockList } from '../configs/super-block-list';
 
-export const indexRoute = (req: Request, res: Response) => {
+export const indexRoute = (req: Request, res: Response): void => {
   res.json(superBlockList);
 };

tools/challenge-editor/api/routes/save-route.ts

@@ -1,7 +1,7 @@
 import { Request, Response } from 'express';
 import { saveStep } from '../utils/save-step';
 
-export const saveRoute = async (req: Request, res: Response) => {
+export const saveRoute = async (req: Request, res: Response): Promise<void> => {
   const { superblock, block, step } = req.params;
   const content = (req.body as { content: string }).content;
 

tools/challenge-editor/api/routes/step-route.ts

@@ -1,7 +1,7 @@
 import { Request, Response } from 'express';
 import { getStepContent } from '../utils/get-step-contents';
 
-export const stepRoute = async (req: Request, res: Response) => {
+export const stepRoute = async (req: Request, res: Response): Promise<void> => {
   const { superblock, block, step } = req.params;
 
   const stepContents = await getStepContent(superblock, block, step);

tools/challenge-editor/api/routes/super-block-route.ts

@@ -1,7 +1,10 @@
 import { Request, Response } from 'express';
 import { getBlocks } from '../utils/get-blocks';
 
-export const superblockRoute = async (req: Request, res: Response) => {
+export const superblockRoute = async (
+  req: Request,
+  res: Response
+): Promise<void> => {
   const sup = req.params.superblock;
 
   const blocks = await getBlocks(sup);

tools/challenge-editor/api/routes/tools-route.ts

@@ -25,7 +25,10 @@ const toolsSwitch: ToolsSwitch = {
   }
 };
 
-export const toolsRoute = async (req: Request, res: Response) => {
+export const toolsRoute = async (
+  req: Request,
+  res: Response
+): Promise<void> => {
   const { superblock, block, command } = req.params;
   const { num } = req.body as Record<string, number>;
   const directory = join(

tools/challenge-editor/api/utils/get-blocks.ts

@@ -4,7 +4,12 @@ import { CHALLENGE_DIR, META_DIR } from '../configs/paths';
 
 import { PartialMeta } from '../interfaces/partial-meta';
 
-export const getBlocks = async (sup: string) => {
+type Block = {
+  name: string;
+  path: string;
+};
+
+export const getBlocks = async (sup: string): Promise<Block[]> => {
   const filePath = join(CHALLENGE_DIR, sup);
 
   const files = await readdir(filePath);

tools/challenge-editor/api/utils/get-step-contents.ts

@@ -7,7 +7,7 @@ export const getStepContent = async (
   sup: string,
   block: string,
   step: string
-) => {
+): Promise<{ name: string; fileData: string }> => {
   const filePath = join(CHALLENGE_DIR, sup, block, step);
 
   const fileData = await readFile(filePath, 'utf8');

tools/challenge-editor/api/utils/get-steps.ts

@@ -10,7 +10,13 @@ const getFileOrder = (id: string, meta: PartialMeta) => {
   return meta.challengeOrder.findIndex(([f]) => f === id);
 };
 
-export const getSteps = async (sup: string, block: string) => {
+type Step = {
+  name: string;
+  id: string;
+  path: string;
+};
+
+export const getSteps = async (sup: string, block: string): Promise<Step[]> => {
   const filePath = join(CHALLENGE_DIR, sup, block);
 
   const metaPath = join(META_DIR, block, 'meta.json');

tools/challenge-editor/api/utils/save-step.ts

@@ -7,7 +7,7 @@ export const saveStep = async (
   block: string,
   step: string,
   content: string
-) => {
+): Promise<boolean> => {
   try {
     const filePath = join(CHALLENGE_DIR, sup, block, step);
 

tools/challenge-helper-scripts/commands.ts

@@ -9,7 +9,7 @@ import {
   updateStepTitles
 } from './utils';
 
-function deleteStep(stepNum: number) {
+function deleteStep(stepNum: number): void {
   if (stepNum < 1) {
     throw 'Step not deleted. Step num must be a number greater than 0.';
   }
@@ -28,7 +28,7 @@ function deleteStep(stepNum: number) {
   console.log(`Sucessfully deleted step #${stepNum}`);
 }
 
-function insertStep(stepNum: number) {
+function insertStep(stepNum: number): void {
   if (stepNum < 1) {
     throw 'Step not inserted. New step number must be greater than 0.';
   }
@@ -56,7 +56,7 @@ function insertStep(stepNum: number) {
   console.log(`Sucessfully inserted new step #${stepNum}`);
 }
 
-function createEmptySteps(num: number) {
+function createEmptySteps(num: number): void {
   if (num < 1 || num > 1000) {
     throw `No steps created. arg 'num' must be between 1 and 1000 inclusive`;
   }

tools/challenge-helper-scripts/utils.ts

@@ -17,7 +17,7 @@ const createStepFile = ({
   stepNum,
   projectPath = getProjectPath(),
   challengeSeeds = {}
-}: Options) => {
+}: Options): ObjectID => {
   const challengeId = new ObjectID();
 
   const template = getStepTemplate({
@@ -36,7 +36,7 @@ interface InsertOptions {
   stepId: ObjectID;
 }
 
-function insertStepIntoMeta({ stepNum, stepId }: InsertOptions) {
+function insertStepIntoMeta({ stepNum, stepId }: InsertOptions): void {
   const existingMeta = getMetaData();
   const oldOrder = [...existingMeta.challengeOrder];
   oldOrder.splice(stepNum - 1, 0, [stepId.toString()]);
@@ -49,7 +49,7 @@ function insertStepIntoMeta({ stepNum, stepId }: InsertOptions) {
   updateMetaData({ ...existingMeta, challengeOrder });
 }
 
-function deleteStepFromMeta({ stepNum }: { stepNum: number }) {
+function deleteStepFromMeta({ stepNum }: { stepNum: number }): void {
   const existingMeta = getMetaData();
   const oldOrder = [...existingMeta.challengeOrder];
   oldOrder.splice(stepNum - 1, 1);
@@ -62,7 +62,7 @@ function deleteStepFromMeta({ stepNum }: { stepNum: number }) {
   updateMetaData({ ...existingMeta, challengeOrder });
 }
 
-const updateStepTitles = () => {
+const updateStepTitles = (): void => {
   const meta = getMetaData();
 
   const fileNames: string[] = [];

tools/scripts/build/schema/trending-schema.ts

@@ -65,6 +65,6 @@ const schema = Joi.object().keys({
 
 export const trendingSchemaValidator = (
   trendingObj: Record<string, string>
-) => {
+): Joi.ValidationResult => {
   return schema.validate(trendingObj);
 };

tools/ui-components/src/color-system/color-system.stories.tsx

@@ -6,6 +6,6 @@ const story = {
   component: AllPalettes
 };
 
-export const ColorSystem = () => <AllPalettes />;
+export const ColorSystem = (): JSX.Element => <AllPalettes />;
 
 export default story;

tools/ui-components/src/color-system/color-system.tsx

@@ -53,7 +53,7 @@ const Palette = ({ colors }: PaletteProps) => {
   );
 };
 
-export const AllPalettes = () => {
+export const AllPalettes = (): JSX.Element => {
   return (
     <>
       <Palette colors={getPaletteByColorName('gray')} />

tools/ui-components/src/form-control/form-control-feedback.tsx

@@ -6,7 +6,7 @@ export const FormControlFeedback = ({
   children,
   className,
   testId
-}: FormControlVariationProps) => {
+}: FormControlVariationProps): JSX.Element => {
   const defaultClasses =
     'absolute top-0 right-0 z-2 block w-8 h-8 leading-8 ' +
     'text-center pointer-events-none text-green-700';

tools/ui-components/src/form-control/form-control-static.tsx

@@ -6,7 +6,7 @@ export const FormControlStatic = ({
   className,
   children,
   testId
-}: FormControlVariationProps) => {
+}: FormControlVariationProps): JSX.Element => {
   const defaultClasses = 'py-1.5 mb-0 min-h-43-px text-foreground-secondary';
 
   const classes = [defaultClasses, className].join(' ');

tools/ui-components/utils/gen-component-script.ts

@@ -8,7 +8,7 @@ if (!name) {
   throw new Error('You must include a component name.');
 }
 
-if (!name.match(/^[A-Z]/)) {
+if (!/^[A-Z]/.exec(name)) {
   throw new Error('Component name must be in PascalCase.');
 }
 

tools/ui-components/utils/gen-component-template.ts

@@ -1,23 +1,23 @@
 // component.tsx
-export const component = (name: string) => `
+export const component = (name: string): string => `
 import React from 'react';
-    
+
 import { ${name}Props } from './types';
-    
+
 export const ${name} = ({}: ${name}Props) => {
   return <div>Hello, I am a ${name} component</div>;
 };
 `;
 
 // types.ts
-export const type = (name: string) => `
+export const type = (name: string): string => `
 export interface ${name}Props {
   className?: string
 }
 `;
 
 // component.test.tsx
-export const test = (name: string) => `
+export const test = (name: string): string => `
 import React from 'react';
 import { render, screen } from '@testing-library/react';
 import userEvent from '@testing-library/user-event';
@@ -30,7 +30,7 @@ describe('<${name} />', () => {
 `;
 
 // component.stories.tsx
-export const story = (name: string) => `
+export const story = (name: string): string => `
 import React from 'react';
 import { Story } from '@storybook/react';
 import { ${name}, ${name}Props } from '.';
@@ -53,7 +53,7 @@ export default story;
 `;
 
 // index.ts
-export const barrel = (name: string, kebabCasedName: string) => `
+export const barrel = (name: string, kebabCasedName: string): string => `
 export { ${name} } from './${kebabCasedName}';
 export type { ${name}Props } from './types';
 `;

utils/get-lines.ts

@@ -1,4 +1,4 @@
-export function getLines(contents: string, range?: number[]) {
+export function getLines(contents: string, range?: number[]): string {
   if (!range) {
     return '';
   }

utils/index.ts

@@ -44,6 +44,8 @@ for (const [id, title] of idToTitle) {
   }
 }
 
-export const getCertIds = () => idToPath.keys();
-export const getPathFromID = (id: string) => idToPath.get(id);
-export const getTitleFromId = (id: string) => idToTitle.get(id);
+export const getCertIds = (): IterableIterator<string> => idToPath.keys();
+export const getPathFromID = (id: string): string | undefined =>
+  idToPath.get(id);
+export const getTitleFromId = (id: string): string | undefined =>
+  idToTitle.get(id);

utils/validate.ts

@@ -1,21 +1,36 @@
-export const invalidCharError = {
+type Valid = {
+  valid: true;
+  error: null;
+};
+
+type Invalid = {
+  valid: false;
+  error: string;
+};
+
+type Validated = Valid | Invalid;
+
+export const invalidCharError: Invalid = {
   valid: false,
   error: 'contains invalid characters'
 };
-export const validationSuccess = { valid: true, error: null };
-export const usernameTooShort = { valid: false, error: 'is too short' };
-export const usernameIsHttpStatusCode = {
+export const validationSuccess: Valid = { valid: true, error: null };
+export const usernameTooShort: Invalid = {
+  valid: false,
+  error: 'is too short'
+};
+export const usernameIsHttpStatusCode: Invalid = {
   valid: false,
   error: 'is a reserved error code'
 };
 
 const validCharsRE = /^[a-zA-Z0-9\-_+]*$/;
-export const isHttpStatusCode = (str: string) => {
+export const isHttpStatusCode = (str: string): boolean => {
   const output = parseInt(str, 10);
   return !isNaN(output) && output >= 100 && output <= 599;
 };
 
-export const isValidUsername = (str: string) => {
+export const isValidUsername = (str: string): Validated => {
   if (!validCharsRE.test(str)) return invalidCharError;
   if (str.length < 3) return usernameTooShort;
   if (isHttpStatusCode(str)) return usernameIsHttpStatusCode;