## What's wrong
This problem is specific to errors that happen on the client _after_ the initial mounting of the component. (The router has special logic to handle exceptions thrown in `getInitialProps` during a client-side navigation, and I've confirmed this logic is correct.)
Specifically, if the page is mounted, and you raise an exception on the page, the exception will cause the error page to be mounted without ever invoking `getInitialProps` on the new App/Error page pairing.
This has been illustrated with multiple repros in #4574.
## Why is it broken
This regression was introduced two months ago in #4156, where the invocation of `getInitialProps` was removed from the app's top-level error handler. Specifically, [this line](https://github.com/zeit/next.js/pull/4156/files#diff-895656aeaccff5d7c0f56a113ede9662L147) was removed and [replaced by a comment](https://github.com/zeit/next.js/pull/4156/files#diff-895656aeaccff5d7c0f56a113ede9662R167) that says that "`App` will handle the calling of `getInitialProps`".
I believe the sentiment about "`App` will handle calling `getInitialProps`" is mistaken. In fact, it really doesn't make sense on its face, since it would require an instance lifecycle method of `App` (which is mounted immediately after the comment) to invoke the `static getInitialProps` method on the error page.
## How I fixed it
I've fixed this in a fork by restoring Lines 146 – 148 that were removed in #4156. I think this is the right fix, but Next.js's handling of `getInitialProps` could certainly be improved. (The code in [this conditional](86d01706a6/client/index.js (L173)) speaks to the unnecessary complexity around this.)
* Handle production errors correctly
* Improved source map support
* Make react-hot-loader hold state again
* Remove console.log
* Load modules on demand
* Catch errors in rewriteErrorTrace
* Update comment
* Update comment
* Remove source-map-support
* Load modules in next-dev
* Make sure error logged has sourcemaps too
* Add tests for production runtime errors
* Add tests for development runtime errors. Fix issue with client side errors in development
* Move functionality back to renderError now that error handling is consistent
* Rename to applySourcemaps
* Layout ground works for next/async
* Implement the Dynamic Bundle feature.
* Add some test cases.
* Update README.
* Implement props aware dynamic bundle API.
* Update tests and README.
* Add a test case for React Context support.
* Always check with the fs when gettings chunks.
* Add a new set of test cases for dynamic imports in dev.
* Add dynamic import test cases for production.
* Add availableChunks support for static exports.
* Introduce script tag based page loading system.
* Call ensurePage only in the dev mode.
* Implement router using the page-loader.
* Fix a typo and remove unwanted code.
* Fix some issues related to rendering.
* Fix production tests.
* Fix ondemand test cases.
* Fix unit tests.
* Get rid of eval completely.
* Remove all the inline code.
* Remove the json-pages plugin.
* Rename NEXT_PAGE_LOADER into __NEXT_PAGE_LOADER__
* Rename NEXT_LOADED_PAGES into __NEXT_LOADED_PAGES__
* Remove some unwanted code.
* Load everything async.
* Remove lib/eval-script.js
We no longer need it.
* Move webpack idle wait code to the page-loader.
Because that's the place to do it.
* Remove pageNotFound key from the error.
* Remove unused error field 'buildError'
* Add much better logic to normalize routes.
* Get rid of mitt.
* Introduce a better way to register pages.
* Came back to the mitt() based page-loader.
* Add link rel=preload support.
* Add assetPrefix support to add support for CDNs.
* Add assetPrefix support for preload links.
* Update readme.md
* Use jest-cli instead of gulp plugin.
* Use jest-cli instead of gulp plugin.
* Move fixtures into the examples dir.
* Move test code of example app to the basic example.
* Add isolated tests for server/resolve
* Allow tests to use cheerio.
* Use portfinder to get a unique port.
* Move back integration tests into the example dir.
* Introduce next-test-utils.
* Remove gulp-jest
* Add coveralls support.
* Use transpiled version of code in dist.
This is to make sure same file gets covered
by both unit/isolated tests and integration tests.
* Add support for source maps.
* Use code from dist always.
* Use nyc to stop instrument.
* Add integration test suite for production usage.
* Use jest-cli.
* Add support for running e2e tests.
* Check gzipPath with fs.stat before serving
Otherwise, serve package might throw issues other than ENOENT
* Install chromedriver with npm install.
* Install chrome on travis-ci.
* Add --forceExit to Jest.
* Run tests only on Node v6.
That's because selenium-webdriver only supports
Node 6 LTS.
* Use chromedriver NPM module to install chromedriver.
* Use wd as the webdriver client.
* Run chromedriver before tests.
* Run travis for both node 4 and 6
* Remove unwanted npm install script.
* Move some common text utilities to next-test-utils
* Add lint checks and testing in npm prepublish hook.
* Use npm on travis-ci.
We are having some caching issues with yarn and chromedriver.
* Make tests work on windows.\n But chromedriver doesn't work.
* Clean up dependencies.
* Run chromedriver in background without any tools.
* Fix a typo in the code.
* Use ES6 features used in node4 inside the gulpfile.
* Add some comments.
* Add support for running in windows.
* Stop chromedriver properly on windows.
* Fix typos.
