对于Mail，我们可以通过下面的代码在浏览器中预览Mailables

For Mail, we can preview Mailables in the browser with the following code.

Route::get('/mailable', function () {
    $invoice = App\Invoice::find(1);
    return new App\Mail\InvoicePaid($invoice);
});

然而Notification类中toMail返回的MailMessage实例，Laravel文档中并没有给出直接方法在浏览器中预览，我们可以采取下面的方法。

However, the MailMessage instance returned by toMail method in the Notification class does not give a direct method to preview in the browser in the Laravel document. We can use the following code.

Route::get('/mailable', function () {
    $message = (new \App\Notifications\FooNotification()->toMail("bar");
    return app()->make(\Illuminate\Mail\Markdown::class)->render($message->markdown, $message->data());
});

在Laravel5.8及以上，MailMessage实现了Renderable接口（PR in Github），所以可以直接return MailMessage实例作为响应了。

In Laravel 5.8 and above, MailMessage implements the Renderable interface (PR in Github), so you can directly return the MailMessage instance as a response.