Fixes #12291 

![image](https://user-images.githubusercontent.com/616428/85499698-176b4900-b5b0-11ea-8a5d-a7f0b4c20307.png)

Added an Example using MongoDB's Realm-Web SDK 

![Screenshot 2020-06-25 at 5 25 49 PM](https://user-images.githubusercontent.com/11258286/85715292-ebafa680-b708-11ea-98bd-d8d64701f0af.png)


Fixes #14417 

Fixes #14464

* avoid pulling code in the bundle for `trailingSlash` logic when it's not enabled
* avoid cloning the url an extra time if normalizing the path doesn't change it

Avoid trailing slashes on urls that look like files. The redirect for `trailingSlash: true` will now look like:

```
Redirects

┌ source: /:path*/:file.:ext/
├ destination: /:path*/:file.:ext
└ permanent: true

┌ source: /:path*/:notfile([^/.]+)
├ destination: /:path*/:notfile/
└ permanent: true
```

The default still looks like:

```
Redirects

┌ source: /:path+/
├ destination: /:path+
└ permanent: true
```
After this gets merged, I have a few optimizations planned on the normalization code that should reduce the client bundle a little and that consolidates the `trailingSlash` and `exportTrailingSlash` options

Fixes #14632
Fixes #14690

Change Data Fetching Method in Example with-mongodb-mongoose
Fetch Data on Runtime (getServerSideProps) rather than Build Time (getStaticProps)

The existing example gives an error on every hot reload, perhaps because of the way that an initial `useEffect` hook imports the `GLTFLoader` and it doesn't redo that on hot reload?

Putting the component using the `useLoader` hook in a dynamic import seems to fix this.

Open to better suggestions, this is kind of awkward to use still...

Closes #14682

This updates `fetchNextData` to re-use the `getDataHref` function from `page-loader` which has more verbose handling to ensure the correct `/_next/data` URL is built. Re-using this logic ensures the `/_next/data` URL can still be built even when a mismatching `href` and `as` value is provided to `next/link`.

This also fixes a case in `getDataHref` where optional values that weren't provided would fail to build the data href since the check requiring the param be present while interpolating the route values hasn't been updated to allow missing params for optional values.

An additional test case has been added to the prerender suite to ensure the `/_next/data` URL is built correctly when mismatching `href` and `as` values are provided

x-ref: https://github.com/vercel/next.js/discussions/14536
x-ref: https://github.com/vercel/next.js/discussions/9081#discussioncomment-31160
Closes: https://github.com/vercel/next.js/issues/14668

Add tests and fix for when the url contains query parameters.
`router` now uses the same method for formatting url+as pair as `Link`, will be able to share code after https://github.com/vercel/next.js/pull/14633 is merged

Preparation for a larger rewrite

We've been meaning to change this code for a while 👍

- Changed the name from spr to incremental
- Changed the code to be a class instead of using module scope variables

Tweak PR stats message for req/sec metrics. I think they should warn when they are negative, not when positive

Closes https://github.com/vercel/next.js/issues/14570
Closes https://github.com/vercel/next.js/issues/14576

- The example features everything on the page in our docs while still being quite simple
- Added a link to it in the documentation
- Deprecated the with-now-env example

Add @prefresh/next as dependency

Closes #14607

Closes [13709](https://github.com/vercel/next.js/issues/13709).

The solution works, **(tested and confirmed with true and false flags with the latest next version)** though I am quite sure this is not the most elegant and proper way to implement it. I have spent the good part of yesterday and today's morning in order to make it more generic but since it's my first time working with anything related to webpack I have struggled miserably. Last, but not least I'm unsure if this is the most proper naming for the flag.

Please, let me know what you want me to change and I'll get it done asap.

Closes https://github.com/vercel/next.js/issues/14596

Makes sure this works correctly with webpack 5.

Fixes https://github.com/vercel/next.js/issues/14573

Closes: #14595

This moves the custom-routes configs outside of the experimental section to prepare them for being made stable

Fixes: https://github.com/vercel/next.js/issues/14184

Keeping up with section headers in markdown is fun :)
Co-authored-by: Nkodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

Simplifies on-demand-entries a bit.

[ch4109]

Closes https://github.com/vercel/next.js/issues/14500

Our current docs for `next/router` use examples from both `useRouter` and `import Router from 'next/router'`, with this PR I'm unifying the API into `useRouter` (`withRouter` is still going to be mentioned multiple times as it is the HOC alternative) and no longer mentioning that you can import a global `Router` object from `next/router`, not sure if I should mention it at least once but that didn't seem to be required.

I also did some structural changes to the docs for `next/router`, now every method starts with a description, then the implementation and explanation of the parameters of the method, and then the usage example, because every method uses the same `Usage` title the hash for them would be something like `#usage`, `#usage-1`, `#usage-2`, e.t.c, so I'm not very happy with this but it looks good.

Feedback wanted 🙏 

Test case for https://github.com/GoogleChromeLabs/native-url/pull/28

Fix https://github.com/vercel/next.js/issues/14419

Noticed while trying to get https://github.com/vercel/next.js/pull/14442 tests to pass. The backslash needs to be double escaped in snapshots. Forward slashes aren't escaped, maybe that was the assumption when this test was written?

Basically this PR adds Next.js 's default TypeScript setting and integrates [@storybook/preset-typescript](https://github.com/storybookjs/presets/tree/master/packages/preset-typescript) into original [with-storybook](https://github.com/vercel/next.js/tree/canary/examples/with-storybook) example. 

However, I thought it may save time for someone who are planning to use storybook with next.js and TypeScript :)

* Avoid adding basePath when it's not needed

When using the `basePath` setting, on pages with params it will fire a router change. This will pass the url pathname in the `as` param using the `getUrl()` function. This means the `as` path will be sent through already including the `basePath`, leading to `/basePath/basePath/path` which will cause the router to throw an error.

* lint

* Add test case and ensure removal

* Make sure to re-add before changeState
Co-authored-by: NJJ Kasper <jj@jjsweb.site>

I accidentally deleted the repo the original PR was based upon haha. 

Anyway, the code was still on my computer so here's a new PR with the same content. 

I addressed the latest comments from @lfades in the old PR (https://github.com/vercel/next.js/pull/14180)

I also updated `next-auth` to `2.1.0` and updated the `<Provider />` component in `_app.js` that needed updating since the latest release.

Let me know if I missed anything else, otherwise I think this should be good to go 👍

* Update index.js

* Update index.js

* Update examples/with-firebase-authentication/pages/index.js
Co-authored-by: NLuis Alvarez D <luis@vercel.com>