Function formatToParts

packages/intl-messageformat/formatters.ts:116–350

(
  els: MessageFormatElement[],
  locales: string | string[],
  formatters: Formatters,
  formats: Formats,
  values?: Record<string, PrimitiveType | T | FormatXMLElementFn<T>>,
  currentPluralValue?: number,
  // For debugging
  originalMessage?: string
)

// TODO(skeleton): add skeleton support
export function formatToParts<T>(
  els: MessageFormatElement[],
  locales: string | string[],
  formatters: Formatters,
  formats: Formats,
  values?: Record<string, PrimitiveType | T | FormatXMLElementFn<T>>,
  currentPluralValue?: number,
  // For debugging
  originalMessage?: string
): MessageFormatPart<T>[] {
  // Hot path for straight simple msg translations
  if (els.length === 1 && isLiteralElement(els[0])) {
    return [
      {
        type: PART_TYPE.literal,
        value: els[0].value,
      },
    ]
  }
  const result: MessageFormatPart<T>[] = []
  for (const el of els) {
    // Exit early for string parts.
    if (isLiteralElement(el)) {
      result.push({
        type: PART_TYPE.literal,
        value: el.value,
      })
      continue
    }
    // TODO: should this part be literal type?
    // Replace `#` in plural rules with the actual numeric value.
    if (isPoundElement(el)) {
      if (typeof currentPluralValue === 'number') {
        result.push({
          type: PART_TYPE.literal,
          value: formatters.getNumberFormat(locales).format(currentPluralValue),
        })
      }
      continue
    }

    const {value: varName} = el

    // Enforce that all required values are provided by the caller.
    if (!(values && varName in values)) {
      throw new MissingValueError(varName, originalMessage)
    }

    let value = values[varName]
    if (isArgumentElement(el)) {
      if (
        !value ||
        typeof value === 'string' ||
        typeof value === 'number' ||
        typeof value === 'bigint'
      ) {
        value =
          typeof value === 'string' ||