Function format

pkgs/core/src/format/index.ts:346–442

(
  date: DateArg<Date> & {},
  formatStr: string,
  options?: FormatOptions,
)

 * //=> "3 o'clock"
 */
export function format(
  date: DateArg<Date> & {},
  formatStr: string,
  options?: FormatOptions,
): string {
  const defaultOptions = getDefaultOptions();
  const locale = options?.locale ?? defaultOptions.locale ?? defaultLocale;

  const firstWeekContainsDate =
    options?.firstWeekContainsDate ??
    options?.locale?.options?.firstWeekContainsDate ??
    defaultOptions.firstWeekContainsDate ??
    defaultOptions.locale?.options?.firstWeekContainsDate ??
    1;

  const weekStartsOn =
    options?.weekStartsOn ??
    options?.locale?.options?.weekStartsOn ??
    defaultOptions.weekStartsOn ??
    defaultOptions.locale?.options?.weekStartsOn ??
    0;

  const originalDate = toDate(date, options?.in);

  if (!isValid(originalDate)) {
    throw new RangeError("Invalid time value");
  }

  let parts: FormatPart[] = formatStr
    .match(longFormattingTokensRegExp)!
    .map((substring) => {
      const firstCharacter = substring[0];
      if (firstCharacter === "p" || firstCharacter === "P") {
        const longFormatter = longFormatters[firstCharacter];
        return longFormatter(substring, locale.formatLong);
      }
      return substring;
    })
    .join("")
    .match(formattingTokensRegExp)!
    .map((substring) => {
      // Replace two single quote characters with one single quote character
      if (substring === "''") {
        return { isToken: false, value: "'" };
      }

      const firstCharacter = substring[0];
      if (firstCharacter === "'") {
        return { isToken: false, value: cleanEscapedString(substring) };
      }

      if (formatters[firstCharacter]) {
        return { isToken: true, value: substring };
      }

      if (firstCharacter.match(unescapedLatinCharacterRegExp)) {
        throw new RangeError(
          "Format string contains an unescaped latin alphabet character `" +