Define WorkboxGlobalScope in workbox-precaching

[jeffposnick]

R: @philipwalton

I'm not 100% sure that this is the right way to do things, so please review this with skepticism, but this definition is the cleanest way I could come up with to support using self.__WB_MANIFEST inside of a TypeScript swSrc file.

The usage ends up looking like:

import {precacheAndRoute, WorkboxGlobalScope} from 'workbox-precaching/precacheAndRoute';

declare const self: WorkboxGlobalScope;

precacheAndRoute(self.__WB_MANIFEST);

Maybe we should have a separate WorkboxGlobalScope declaration inside of workbox-core instead, which would presumably make it cleaner if we ever added in custom global properties that weren't related to workbox-precaching?

[philipwalton]

Yeah, In think it would be cleaner to add this to workbox-core/types (and possibly more future-friendly, as you say).

BTW, I spent a bit of time trying to make this work without the user having to import anything, and I couldn't make it work (without referencing self.__WB_MANIFEST in the source, which I don't think we want). I think it could work if the SW global was properly set by TypeScript, but I guess we'll have to wait and see.

[philipwalton]

E.g. lit-html does something similar, but I believe that's only working because they're referencing the property in their source: https://github.com/Polymer/lit-html/blob/47a8af4805d775614fe075975eba2c3f6e521a04/src/lit-html.ts#L50-L54

[jeffposnick]

Thanks for the tip regarding lit-html's usage. I think the magic here is the declare global {} wrapper around the interface.

With this latest commit, it looks like it just adds in support for the __WB_MANIFEST property as a side-effect of importing one of the precaching modules, and there's not requirement that I set self.__WB_MANIFEST to any value in the TypeScript source.

Given that this approach works, I'm thinking it makes more sense to keep it scoped tightly to the actual modules in which the additional properties will actually be used, rather than in workbox-core. If we need to extend ServiceWorkerGlobalScope with new properties in multiple places I believe that they're all considered additive, rather than overwriting each other.

[philipwalton]

I see, so you're thinking of doing this but still expecting users to have to do this in their own code, correct?

declare var self: ServiceWorkerGlobalScope;

That seems fine to me, but note it's probably the case that many Workbox users wouldn't otherwise have to do declare var self: ServiceWorkerGlobalScope since they're likely not using self anywhere (they're using Workbox APIs).

Given that I wonder if it makes sense to also extend WorkerGlobalScope?

[coveralls]

Coverage remained the same at 77.688% when pulling 4665c0d on workbox-global-scope into bd6edce on master.

[jeffposnick]

I've switched to extending WorkerGlobalScope.

[workbox-pr-bot]

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packages/workbox-window/build/workbox-window.dev.umd.js	31.88 KB	31.88 KB	-0%	8.10 KB

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File	Before	After	Change	GZipped
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packages/workbox-streams/build/workbox-streams.prod.js	1.46 KB	1.46 KB	0%	720 B
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packages/workbox-webpack-plugin/build/inject-manifest.js	4.67 KB	4.67 KB	0%	1.59 KB
packages/workbox-window/build/workbox-window.dev.umd.js	31.88 KB	31.88 KB	-0%	8.10 KB
packages/workbox-window/build/workbox-window.prod.umd.js	4.46 KB	4.46 KB	0%	1.84 KB

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3.49KB gzip'ed (23% of limit)
7.8KB uncompressed