await when condition end (typescript)

when.ts

export const when = (
  condition: () => boolean | Promise<boolean>,
  timeoutMs = 0,
  repeatMs = 500
) => {
  return new Promise<void>((resolve) => {
    const startTime = Date.now()
    const checkFlag = async () => {
      if (await condition()) {
        resolve()
      } else if (timeoutMs !== 0 && Date.now() > startTime + timeoutMs) {
        resolve()
      } else {
        window.setTimeout(checkFlag, repeatMs)
      }
    }
    checkFlag()
  })
}