Update to TypeScript 4.3

[jtpio]

Update the typescript dependency to the latest version.

Leaving as a draft for now as there might be some breaking changes to fix.

[github-actions]

👈 Launch a binder notebook on branch jtpio/ipywidgets/ts-42

[jtpio]

One of the changes introduced in TypeScript 4.0 is causing compilation to fail with:

Error: src/widget.ts(187,14): error TS2790: The operand of a 'delete' operator must be optional.
Error: src/widget.ts(193,12): error TS2790: The operand of a 'delete' operator must be optional.
Error: src/widget.ts(760,12): error TS2790: The operand of a 'delete' operator must be optional.
Error: src/widget.ts(798,12): error TS2790: The operand of a 'delete' operator must be optional.

https://devblogs.microsoft.com/typescript/announcing-typescript-4-0/#operands-for-delete-must-be-optional

Which corresponds to:

ipywidgets/packages/base/src/widget.ts

Line 187 in f085739

delete this.comm;

[jtpio]

Adding to the 8.0 milestone for consideration as this might result in changes in public interfaces and typings.

[jtpio]

One of the changes introduced in TypeScript 4.0 is causing compilation to fail with:

Another change is related to properties overriding accessors (TS2610) in 4.0:

https://devblogs.microsoft.com/typescript/announcing-typescript-4-0/#properties-overriding-accessors-and-vice-versa-is-an-error

For example:

Error: src/widget_box.ts(139,3): error TS2610: 'pWidget' is defined as an accessor in class 'DOMWidgetView', but is overridden here in 'BoxView' as an instance property.

Link to a TypeScript playground for reference:

https://www.typescriptlang.org/play?ts=4.2.3#code/MYGwhgzhAEBCkFNoG8BQ1oBcwHMByYAtggPwBc0EmATgJYB2OA3KgL6qqiQwAiCdANwQATaAgAemBPWEx4EJGgw4EmLLgLEAFAEoU6DNGqqArtXrQA5ACMTmTAHt6llhnasgA

[jasongrout]

I updated to TS 4.3 and fixed the errors.

[jasongrout]

@jtpio: your commits look good. Can you review my commits, and merge if they look good?

[jasongrout]

(or @vidartf or anyone else, feel free to review all of our commits and merge if they look good :)

[jtpio]

Thanks Jason for picking this up!

[jtpio]

Just to double check: this backbone update was required to grab the new preinitialize method? (and then fix the TS error)

[jtpio]

Yes looks like it's mentioned in the change log on https://backbonejs.org:

[jtpio]

Just checked the diff, quickly tried on Binder and it looks good 👍 Thanks!

Leaving it open one more day in case someone else also wants to have a look, and then we should be able to merge it.

[jtpio]

Thanks!