infer return type of functions

helpers/array.ts

@@ -1,4 +1,4 @@
-export function getNextSmaller<T>(array: T[], pivot: T) {
+export function getNextSmaller<T>(array: T[], pivot: T): T {
   if (!array || !Array.isArray(array) || !array.length) {
     return null
   }
@@ -9,7 +9,7 @@ export function getNextSmaller<T>(array: T[], pivot: T) {
     .find((item) => item < pivot)
 }
 
-export function getNextBigger<T>(array: T[], pivot: T) {
+export function getNextBigger<T>(array: T[], pivot: T): T {
   if (!array || !Array.isArray(array) || !array.length) {
     return null
   }

helpers/bill.ts

@@ -1,11 +1,11 @@
 import { MILAGE_TARIFS } from '../db/enums'
 import { AdditionalCost } from '../db/bill'
 
-function roundToCent(amount: number) {
+function roundToCent(amount: number): number {
   return Math.round(amount * 100) / 100
 }
 
-export function getMilageCosts(tarif: MILAGE_TARIFS, km: number): number {
+export function getMilageCosts({ tarif, km }: { tarif: MILAGE_TARIFS; km: number }): number {
   if (tarif === MILAGE_TARIFS.NOCHARGE) {
     return 0
   }
@@ -56,7 +56,7 @@ export function getBillTotal({
   milage?: number
   additionalCosts: AdditionalCost[]
 }): number {
-  const milageCosts = getMilageCosts(tarif, milage)
+  const milageCosts = getMilageCosts({ tarif, km: milage })
   const additionalCostsSum = additionalCosts
     .map(({ value }) => value)
     .reduce((acc: number, value: number) => acc + value, 0)

helpers/date.ts

@@ -4,7 +4,7 @@ import { utcToZonedTime } from 'date-fns-tz'
 const FRONTEND_FORMAT = 'dd.MM.yyyy'
 const BACKEND_FORMAT = 'yyyy-MM-dd'
 
-export function daysFormatFrontend(days: string[]) {
+export function daysFormatFrontend(days: string[]): string {
   if (days.length === 0) {
     return ''
   }
@@ -24,7 +24,7 @@ export function getDays({
 }: {
   startDate: Date
   endDate: Date
-}) {
+}): string[] {
   let currentDay = new Date(startDate.getTime())
   const days = [dateFormatBackend(currentDay)]
 
@@ -40,22 +40,22 @@ export function getDays({
   return days
 }
 
-function dateFormat(date: Date, formatString: string) {
+function dateFormat(date: Date, formatString: string): string {
   if (!date) {
     return null
   }
   return format(date, formatString)
 }
 
-export function dateFormatBackend(date: Date) {
+export function dateFormatBackend(date: Date): string {
   return dateFormat(date, BACKEND_FORMAT)
 }
 
-export function dateFormatFrontend(date: Date) {
+export function dateFormatFrontend(date: Date): string {
   return dateFormat(date, FRONTEND_FORMAT)
 }
 
-function dateParse(input: string, formatString: string) {
+function dateParse(input: string, formatString: string): Date {
   const date = parse(input, formatString, new Date())
   if (date.getTime() !== NaN) {
     return date
@@ -64,11 +64,11 @@ function dateParse(input: string, formatString: string) {
   return null
 }
 
-export function dateParseFrontend(input: string) {
+export function dateParseFrontend(input: string): Date {
   return dateParse(input, FRONTEND_FORMAT)
 }
 
-export function nowInTz(timezone = 'Europe/Berlin') {
+export function nowInTz(timezone = 'Europe/Berlin'): Date {
   const now = new Date()
   return utcToZonedTime(now, timezone)
 }

helpers/ical.ts

@@ -38,7 +38,7 @@ Buchungs-Link: ${getBaseURL()}/booking/${booking.uuid}
   return value
 }
 
-export function generateBookedCalendar(bookings: Booking[]) {
+export function generateBookedCalendar(bookings: Booking[]): string {
   const events = bookings.map((booking) => ({
     productId: 'app.vercel.pfadi-bussle/ics',
     calName: 'Pfadi-Bussle Buchungen',

helpers/mail.ts

@@ -31,7 +31,7 @@ Pfadi Bussle Wart
 Tel. 0151/212 253 62
 `
 
-function getReceivedBookingBookerText(booking: Booking) {
+function getReceivedBookingBookerText(booking: Booking): string {
   return `Hallo liebe/r ${booking.booker.name},
 
 Vielen Dank für Deine Buchungsanfrage zum ${daysFormatFrontend(booking.days)}!
@@ -48,7 +48,7 @@ ${footer}
 `
 }
 
-function getBookingConfirmedText(booking: Booking) {
+function getBookingConfirmedText(booking: Booking): string {
   return `Hallo liebe/r ${booking.booker.name},
 
 deine Buchunganfrage zum ${daysFormatFrontend(
@@ -64,7 +64,7 @@ einsehen und stornieren.
 ${footer}
 `
 }
-function getBookingRejectedText(booking: Booking) {
+function getBookingRejectedText(booking: Booking): string {
   return `Hallo liebe/r ${booking.booker.name},
 
 es tut uns leid aber deine Buchungsanfrage zum ${daysFormatFrontend(
@@ -78,7 +78,7 @@ ${footer}
 `
 }
 
-function getReceivedBookingAdminText(booking: { uuid: string }) {
+function getReceivedBookingAdminText(booking: { uuid: string }): string {
   return `Hallo lieber Admin,
 
 es ging folgende Buchung ein: ${getBaseURL()}/admin/booking/${booking.uuid}
@@ -86,7 +86,7 @@ es ging folgende Buchung ein: ${getBaseURL()}/admin/booking/${booking.uuid}
 MfG`
 }
 
-export async function sendReceivedBookingAdminMail(booking: Booking) {
+export async function sendReceivedBookingAdminMail(booking: Booking): Promise<void> {
   try {
     await sendMail({
       to: [{ email: ADMIN_EMAIL }],
@@ -102,7 +102,7 @@ export async function sendReceivedBookingAdminMail(booking: Booking) {
   }
 }
 
-export async function sendReceivedBookingBookerMail(booking: Booking) {
+export async function sendReceivedBookingBookerMail(booking: Booking): Promise<void> {
   try {
     await sendMail({
       to: [{ email: booking.booker.email, name: booking.booker.name }],
@@ -118,7 +118,7 @@ export async function sendReceivedBookingBookerMail(booking: Booking) {
   }
 }
 
-export async function sendBookingConfirmed(booking: Booking) {
+export async function sendBookingConfirmed(booking: Booking): Promise<void> {
   try {
     await sendMail({
       to: [{ email: booking.booker.email, name: booking.booker.name }],
@@ -143,7 +143,7 @@ export async function sendBookingConfirmed(booking: Booking) {
   }
 }
 
-export async function sendBookingRejected(booking: Booking) {
+export async function sendBookingRejected(booking: Booking): Promise<void> {
   try {
     await sendMail({
       to: [{ email: booking.booker.email, name: booking.booker.name }],
@@ -175,7 +175,7 @@ async function sendMail({
     type?: string
     filename: string
   }[]
-}) {
+}): Promise<void> {
   const data = {
     personalizations: [
       {