Function formatMessage

packages/intl/message.ts:105–247

(
  {
    locale,
    formats,
    messages,
    defaultLocale,
    defaultFormats,
    fallbackOnEmptyString,
    onError,
    timeZone,
    defaultRichTextElements,
  },
  state,
  messageDescriptor = {id: ''},
  values,
  opts
)

) => T extends string ? string : Array<T | string> | string | T

export const formatMessage: FormatMessageFn<any> = (
  {
    locale,
    formats,
    messages,
    defaultLocale,
    defaultFormats,
    fallbackOnEmptyString,
    onError,
    timeZone,
    defaultRichTextElements,
  },
  state,
  messageDescriptor = {id: ''},
  values,
  opts
) => {
  const {id: msgId, defaultMessage} = messageDescriptor

  // `id` is a required field of a Message Descriptor.
  invariant(
    !!msgId,
    `[@formatjs/intl] An \`id\` must be provided to format a message. You can either:
1. Configure your build toolchain with [babel-plugin-formatjs](https://formatjs.github.io/docs/tooling/babel-plugin)
or [@formatjs/ts-transformer](https://formatjs.github.io/docs/tooling/ts-transformer) OR
2. Configure your \`eslint\` config to include [eslint-plugin-formatjs](https://formatjs.github.io/docs/tooling/linter#enforce-id)
to autofix this issue`
  )
  const id = String(msgId)
  const message =
    // In case messages is Object.create(null)
    // e.g import('foo.json') from webpack)
    // See https://github.com/formatjs/formatjs/issues/1914
    messages &&
    Object.prototype.hasOwnProperty.call(messages, id) &&
    messages[id]

  // IMPORTANT: Hot path if `message` is AST with a single literal node
  if (
    Array.isArray(message) &&
    message.length === 1 &&
    message[0].type === TYPE.literal
  ) {
    return message[0].value
  }

  values = {
    ...defaultRichTextElements,
    ...values,
  }
  formats = deepMergeFormatsAndSetTimeZone(formats, timeZone)
  defaultFormats = deepMergeFormatsAndSetTimeZone(defaultFormats, timeZone)

  if (!message) {
    if (fallbackOnEmptyString === false && message === '') {
      return message
    }