try-catch-finally, sync and async

try-catch.ts

/** A `try-catch-finally` that works for both sync and async callbacks. */
export function tryCatch<T>(
  cb: () => T | Promise<T>,
  options: { catch?: (error: unknown) => T; finally?: () => void }
): T {
  const { catch: onCatch, finally: onFinally } = options
  let isAsync = false
  try {
    const result = cb()
    if (isPromise(result)) {
      let promise = result as Promise<T>
      isAsync = true
      if (onCatch) {
        promise = promise.catch(onCatch)
      }
      if (onFinally) {
        promise = promise.finally(onFinally)
      }
      return promise as T
    } else {
      return result
    }
  } catch (err) {
    // if it threw, it can't be async.
    if (onCatch) {
      return onCatch(err)
    } else {
      throw err
    }
  } finally {
    if (onFinally && !isAsync) {
      onFinally()
    }
  }
}

function isPromise(result: unknown): result is Promise<unknown> {
  return !!(
    result &&
    typeof result === 'object' &&
    'then' in result &&
    typeof result.then === 'function'
  )
}