@alubbe @Siemienik Awesome work you guys have put in here! It's time to publish again - this PR making for major version. Is there anything else you think should go in first?
PS. Hope you are all keeping well during this pandemic.

I think we have everything on master to deploy one last bugfix release on v3, and then we should merge #1142 and #1135 (in that order) to push out v4

@alubbe @Siemienik just a couple of questions...
This PR here is a breaking change (dropping an API function) so will mean a major version (i.e. v4), Given that #1142 and #1135 are the way forward, do we want to merge them before v4 or wait for v5?

I noticed somewhere along the line about 22 days ago that the .travis.yml file got dropped - was this intentional?

This PR itself is not backwards incompatible, it just adds warnings, so this can still be released as v3.
After releasing the last v3 release (there are a lot bugfixes on master that should get released), we should werge #1142 and #1135 (in that order) and published 4.0.0. We've been using my branch in production on huge excel files for a few weeks now and haven't had any issues so far.

We've dropped travis to use github actions instead, and we've greatly increased the amount of things we test and platforms we test on (see https://github.com/exceljs/exceljs/pull/1190/files)

We planned to publish it in v3,

I noticed somewhere along the line about 22 days ago that the .travis.yml file got dropped - was this intentional?

I added github workflow for checking if index.d.ts is compiled correctly:
#1182

But it has side-effect - it's turn off Travis checks

So @alubbe made this PR with migration from travis to github workflows: #1190

@guyonroche @alubbe @Siemienik I have to say your work is great, but I found that there are still some problems with index.d.ts.

1. The file is too large, which is not conducive to maintenance and use, and should be split according to the module
2. The file is missing a type declaration, for example: WorkbookReader, WorksheetWriter, WorksheetReader, etc.
3. Private methods should not be exposed, for example: addWorkbookRels, addWorkbook and addSharedStrings in WorkbookWriter

This is the pain point of exceljs, and it has caused a lot of trouble to developers. Personally, before releasing the main version, we should review index.d.ts and solve the above problems. Waht do you think?

I'm not a TS user myself, so I have no idea about any of this - but personally, I think we've never guaranteed that index.d.ts works perfectly, so I think doing those fixes (which sound great) can be done after publishing 4.0.0. I would just really for us to publish 4.0.0 soon, since the open PRs are pretty big

Well, I will be a big fan of migrating to TS (with --allowJs) and step by step move our logic form js files to ts 😄

I feel a big lack of types, now I have to investigate the whole project to do something because IDE doesn't provide intellisense😭.

I wonder about create milestones, fo version 4.1, 4.2 and 5. It should help us to keep one vision of further developing this library.

What is your opinion?

I'd also like us to move to Typescript, but
a) I don't think we should delay moving to 4.0.0
b) let's create a new issue to discuss typescript/index.d.ts instead of discussing here on this closed issue ;)
oh, and I won't be able to help with this effort at all :D