ts format

src/format.ts

@@ -0,0 +1,38 @@
+/* eslint-disable  @typescript-eslint/no-explicit-any */
+import {format as isoFormat} from "isoformat";
+import {string} from "./options.js";
+import {memoize1} from "./memoize.js";
+
+
+const numberFormat = memoize1<Intl.NumberFormat>((locale: string | string[] | undefined) => new Intl.NumberFormat(locale));
+const monthFormat = memoize1<Intl.DateTimeFormat>((locale: string | string[] | undefined, month: "numeric" | "2-digit" | "long" | "short" | "narrow" | undefined) => new Intl.DateTimeFormat(locale, {timeZone: "UTC", month}));
+const weekdayFormat = memoize1<Intl.DateTimeFormat>((locale: string | string[] | undefined, weekday: "long" | "short" | "narrow" | undefined) => new Intl.DateTimeFormat(locale, {timeZone: "UTC", weekday}));
+
+export function formatNumber(locale = "en-US"): (value: any) => string | undefined {
+  const format = numberFormat(locale);
+  return (i: any) => i != null && !isNaN(i) ? format.format(i) : undefined;
+}
+
+export function formatMonth(locale = "en-US", month: "numeric" | "2-digit" | "long" | "short" | "narrow" | undefined = "short") {
+  const format = monthFormat(locale, month);
+  return (i: Date | number | null | undefined) => i != null && !isNaN(i = +new Date(Date.UTC(2000, +i))) ? format.format(i) : undefined;
+}
+
+export function formatWeekday(locale = "en-US", weekday: "long" | "short" | "narrow" | undefined = "short") {
+  const format = weekdayFormat(locale, weekday);
+  return (i: Date | number | null | undefined) => i != null && !isNaN(i = +new Date(Date.UTC(2001, 0, +i))) ? format.format(i) : undefined;
+}
+
+export function formatIsoDate(date: Date): string {
+  return isoFormat(date, "Invalid Date");
+}
+
+export function formatAuto(locale = "en-US"): (value: any) => string | number | undefined {
+  const number = formatNumber(locale);
+  return (v: any) => (v instanceof Date ? formatIsoDate : typeof v === "number" ? number : string)(v);
+}
+
+// TODO When Plot supports a top-level locale option, this should be removed
+// because it lacks context to know which locale to use; formatAuto should be
+// used instead whenever possible.
+export const formatDefault = formatAuto();

src/isoformat.d.ts

@@ -0,0 +1,4 @@
+declare module 'isoformat' {
+    export function format(value: any, fallback: string): string;
+    export function format(value: any, fallback: any): any;
+}