我有一个 MEAN 应用。因为 Angular 是节点应用程序的一部分。 我早些时候在 heroku 上部署了类似的测试应用程序，没有任何错误。但现在应用程序已部署。它不会抛出任何错误。但是，它显示一个空白页面。
知道我应该在哪里查找潜在问题吗？
heroku日志如下
2021-02-22T12:39:31.000000+00:00 app[api]: Build succeeded
2021-02-22T12:39:34.563498+00:00 heroku[web.1]: Starting process with command `node server.js`
2021-02-22T12:39:40.900120+00:00 heroku[web.1]: State changed from starting to up
2021-02-22T12:39:40.698061+00:00 app[web.1]: (node:4) Warning: Accessing non-existent property 'MongoError' of module exports inside circular dependency
2021-02-22T12:39:40.698072+00:00 app[web.1]: (Use `node --trace-warnings ...` to show where the warning was created)
2021-02-22T12:39:40.699628+00:00 app[web.1]: (node:4) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
2021-02-22T12:39:40.739962+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:40.780112+00:00 app[web.1]: (node:4) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
2021-02-22T12:39:42.135480+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.140642+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.141186+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.141422+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.141633+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.141838+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.142012+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.142158+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.142301+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.142446+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.143103+00:00 app[web.1]: (node:4) DeprecationWarning: Listening to events on the Db class has been deprecated and will be removed in the next major version.
2021-02-22T12:39:42.148343+00:00 app[web.1]: Top-level use of w, wtimeout, j, and fsync is deprecated. Use writeConcern instead.
2021-02-22T12:39:42.179697+00:00 app[web.1]: (node:4) DeprecationWarning: collection.ensureIndex is deprecated. Use createIndexes instead.
2021-02-22T12:39:42.181382+00:00 app[web.1]: Connected to database.