This patch updates the minimum supported environments as follows:
- Node.js 16, which was released on 2021-04-20; see https://en.wikipedia.org/wiki/Node.js#Releases
Note also that Node.js 14 will very soon reach EOL, and thus no longer receive any security updates.
This further extends the web-specific import maps introduced in PR 16009, to allow removing *most* of the build-time `require` statements from the viewer. The few remaining ones are fallbacks used for the COMPONENTS respectively the `legacy` GENERIC builds.
After the compatibility updates in PR 15968 it's no longer strictly necessary to build the `viewer.css` file in order for the *development viewer* to work in Chromium-based browsers.
*Please note:* Given that Chromium-based browsers still don't support the *unprefixed* `mask-image` property the icons won't look right, however the development viewer itself works.
Given that Firefox is the *primary* development target, and that running `gulp generic` locally will generate polyfilled CSS, it seems reasonable to make this simplification here.
Given that the GV-viewer isn't using most of the UI-related components of the default-viewer, we can avoid including them in the *built* viewer to save space.[1]
The least "invasive" way of implementing this, at least that I could come up with, is to leverage import maps with suitable stubs for the GV-viewer.
The one slightly annoying thing is that we now have larger import maps across multiple html-files, and you'll need to remember to update all of them when making future changes.
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[1] With this patch, the built `viewer.js` size is 391 kB and `viewer-geckoview.js` is 285 kB.
Until just recently the only existing `Path2D` polyfill didn't have support for Node.js and/or the `node-canvas` package. Given that this was just fixed, in the latest version, we can now finally remove our inline-checks at the relevant call-sites; please also see https://github.com/nilzona/path2d-polyfill#usage-with-node-canvas
Fewer dependencies shouldn't be a bad idea in general, and given that the `node-canvas` package already include a `DOMMatrix` polyfill we can simply use that one instead.
In the `legacy`-builds we (obviously) support the currently maintained Firefox ESR version, and looking at the [release history](https://wiki.mozilla.org/Release_Management/Calendar) those are officially supported (by Mozilla) for about 1-1.5 years.
However, for non-Firefox browsers the `legacy`-builds currently attempt to "support" browsers that are approximately *three* years old.[1] Historically, in the PDF.js project, trying to support old browsers have caused some maintenance problems and even delayed adoption of new web-platform features/functionality.
To lessen the support burden, given that the primary purpose of the PDF.js library is still to develop the *built-in* Firefox PDF Viewer, this patch proposes that the upcoming *major* release changes the minimum supported browsers/environments as follows:
- Chrome 85, which was released on 2020-08-25; see https://en.wikipedia.org/wiki/Google_Chrome_version_history
- Firefox ESR (as before); see https://wiki.mozilla.org/Release_Management/Calendar
- Safari 14, which was released on 2020-09-16; see https://en.wikipedia.org/wiki/Safari_version_history#Safari_14
- Node.js 14 (as before), which is now explicitly listed to prevent it from accidentally breaking; see https://en.wikipedia.org/wiki/Node.js#Releases
---
[1] In older browsers some functionality may not be available and generally we'll ask users to update to a modern browser when bugs, specific to old browsers, are being reported.
The [official Chrome extension](https://chrome.google.com/webstore/detail/pdf-viewer/oemmndcbldboiebfnladdacbdfmadadm) has unfortunately not been updated for *three years*, which means that it's currently missing out on years worth of bug fixes, performance improvements, and new features.
In particular, the Chrome extension suffers from a known bug with non-embedded standard fonts; see issue 13669 for details.
For the time being, this patch proposes that we *temporary* make the following changes:
- Remove the mention of the official Chrome extension from the main README, since it seems unfortunate to somewhat prominently recommend users an old and partially non-working extension.
- Don't run the `gulp lint-chromium` task as part of the CI, since in addition to the official extension not having been updated its code is also not being actively maintained.[1]
Once the official Chrome extension has been updated, and it's being actively maintained again, this patch should be simple enough to revert.
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[1] The last commits, which aren't e.g. linting or general code-maintenance related, happened a year ago now.
Given that the official Bower website, since almost five years, has been advising users to utilize other tools it doesn't seem entirely necessary to keep including the `bower.json` file in the `pdfjs-dist` repository; see e.g. https://bower.io/blog/2017/how-to-migrate-away-from-bower/
Currently we simply use the Babel `preset-env` in the `legacy`-builds of the PDF.js library. This has the side-effect of transpiling the code for *very old* browsers/environments, including ones that we (since many years) no longer support which unnecessarily bloats the size of the `legacy`-builds.
For the CSS files we're only targeting *the supported browsers*, and it's thus possible to extend that to also apply to Babel.
One of the most significant changes, with this patch, is that we'll no longer polyfill `async`/`await` in the `legacy`-builds. However, this shouldn't be an issue given the browsers that we currently support in PDF.js; please refer to:
- https://github.com/mozilla/pdf.js/wiki/Frequently-Asked-Questions#faq-support
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function#browser_compatibility
Note that these cases, which are all in older code, were found using the [`unicorn/no-for-loop`](https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/no-for-loop.md) ESLint plugin rule.
However, note that I've opted not to enable this rule by default since there's still *some* cases where I do think that it makes sense to allow "regular" for-loops.
Rather than including all of this external code in the PDF.js repository, we should be using the npm package instead.
Unfortunately this is slightly more complicated than you'd hope, since the `fit-curve` package (which is older) isn't directly compatible with modern JavaScript modules.
In particular, the following cases needed to be considered:
- For the development viewer (i.e. `gulp server`) and the unit-tests, we thus need to build a fitCurve-bundle that can be directly `import`ed.
- For the actual PDF.js build-targets, we can slightly reduce the sizes by depending on the "raw" `fit-curve` source-code.
- For the Node.js unit-tests, the `fit-curve` package can be used as-is.
*Please note:* The dates below are still a little ways off, however that obviously won't affect the existing PDF.js releases. Hence I think that we can make these changes now, since by the time of the *next* official PDF.js release they'll likely match up pretty well.[1]
While we "support" some (by now) fairly old browsers, that essentially means that the library (and viewer) will load and that the basic functionality will work as intended.[2]
However, in older browsers, some functionality may not be available and generally we'll ask users to update to a modern browser when bugs (specific to old browsers) are reported.[3]
Since we've previously settled on only supporting browsers/environments that are approximately *three years old*, this patch updates the minimum supported browsers/environments as follows:
- Chrome 76, which was released on 2019-07-30; see https://en.wikipedia.org/wiki/Google_Chrome_version_history
- Firefox ESR (as before); see https://wiki.mozilla.org/Release_Management/Calendar
- Safari 13, which was released on 2019-09-19; see https://en.wikipedia.org/wiki/Safari_version_history#Safari_13
- Node.js 14, which was release on 2020-04-21 (all older versions have reached EOL); see https://en.wikipedia.org/wiki/Node.js#Releases
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[1] Given that the releases usually happen every two to three months.
[2] Assuming that a `legacy/`-build is being used, of course.
[3] In general it's never a good idea to use old/outdated browsers, since those may contain *known* security vulnerabilities.
In PR 14710 we only included the JavaScript-part of the polyfill, however we probably need to include the CSS as well to reduce the risk of problems in older browsers.
With the recent CSS-related improvements in the `preprocess`-function we could probably have included this conditionally in the `viewer.css` file. However, considering that the `<dialog>` polyfill-code is only invoked when actually needed it seemed most appropriate/correct to lazy-load the polyfill-CSS as well.
An old shortcoming of the `preprocessCSS`-function is its complete lack of support for our "normal" defines, which makes it very difficult to have build-specific CSS rules. Recently we've started using specially crafted comments to remove CSS rules from the MOZCENTRAL build, but (ab)using the `preprocessCSS`-function in this way really doesn't feel great.
However, it turns out to be surprisingly simple to instead use the "regular" `preprocess`-function for the CSS files as well. The only special-handling that's still necessary is the helper-function for dealing with CSS-imports, but apart from that everything seems to just work.
One reason, as far as I can tell, for having a separate `preprocessCSS`-function was likely that we originally used *lots* of vendor-prefixed CSS rules in our CSS files. With improvements over the years, especially thanks to Autoprefixer and PostCSS, we've been able to remove *almost* all non-standard CSS rules and the need for special-casing the CSS parsing has mostly vanished.
*Please note:* As part of testing this patch I've diffed the output of `gulp generic`, `gulp mozcentral`, and `gulp chromium` against the `master`-branch to check that there was no obvious breakage.
There are two notable changes here:
- `dommatrix` is a major version upgrade, but looking through the commit
history of their `package.json` file at https://github.com/thednp/dommatrix/commits/master/package.json
(due to the lack of a changelog) I couldn't find any breaking changes.
- `es-module-shims` is a regular update, but it was previously pinned
for causing intermittent breakage when running the unit tests in a
browser manually. Fortunately this cannot be reproduced anymore with
the most recent version, so we can also put the caret back now.
Note how both of the openFile-buttons are always hidden during viewer initialization in the MOZCENTRAL build, i.e. the *built-in* Firefox PDF Viewer. Despite that we still include HTML, CSS, and JavaScript code for these buttons in the build.
This patch *reduces* the size of the `gulp mozcentral` output by `1679` bytes, which isn't a lot but still cannot hurt.
Given that we're no longer, after PR 14560, bundling the `web-streams-polyfill`-code in the `legacy`-builds we shouldn't need to exclude it from Babel now.
Given that none of these CSS rules are used at all, unless debugging is enabled, it seems completely unnecessary to load them *unconditionally* for all users.[1]
Note that if *both* the `textLayer` and `pdfBug` debugging hash-parameters are specified simultaneously, we'll now load the `PDFBug`-file *twice* (since the code is simpler that way). However, given first of all that none of this is enabled by default and secondly that using those parameters together isn't helpful[2], potentially loading that file twice is hopefully not an issue.
For the `gulp mozcentral` target, the size of the *built* `viewer.css` file is reduced `> 3%` with this patch.
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[1] For the Firefox built-in PDF Viewer, in order to even be able to access the `PDFBug` functionality, you need to first of all set `pdfjs.pdfBugEnabled = true` manually in `about:config`. Secondly, you then also need to append the `pdfBug=...` hash-parameter to the URL when *initially* loading the document.
[2] Note how the `textLayer`-settings are already, since essentially forever, overriding the highlighting-features of the "FontInspector"-tab.
The various functionality in `web/debugger.js` is currently *indirectly* added to the global scope, since that's how `var` works when it's used outside of any functions/closures.
Given how this functionality is being accessed/used, not just in the viewer but also in the API and textLayer, simply converting the entire file to a module isn't trivial[1]. However, we can at least export the `PDFBug`-part properly and then `import` that dynamically in the viewer.
Also, to improve the code a little bit, we're now *explicitly* exporting the necessary functionality globally.
According to MDN, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#browser_compatibility, all the browsers that we now support have dynamic `imports` implementations.
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[1] We could probably pass around references to the necessary functionality, but given how this is being used I'm just not sure it's worth the effort. Also, adding *official* support for these viewer-specific debugging tools in the API feels both unnecessary and unfortunate.
Rather than *manually* specifying a "mode", we can simply use the regular `defines` directly instead. To improve consistency, in the `external/builder/builder.js` file, a couple of parameters are also re-named.
To allow using modern CSS features that currently only Mozilla Firefox supports[1], while still enabling development/testing in recent Google Chrome versions, we'll have to start building the `web/viewer.css` file with `gulp server` as well.
In my testing, building the development CSS (and copying the images) takes *less than* `200 ms` on average which is hopefully an acceptable overhead for this sort of feature.
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[1] In particular `float`, with `inline-start`/`inline-end` values.
Every single call-site has always passed in `true` for this parameter, ever since the function was first added back in PR 8023. Hence the parameter appears to be completely unnecessary, which is why it's removed and the function is updated to *unconditionally* strip out any license headers (in the middle of the file).
According to the MDN compatibility data, see https://developer.mozilla.org/en-US/docs/Web/API/DOMMatrix/DOMMatrix#browser_compatibility, all browsers that we support have native `DOMMatrix` implementations (since quite some time too).
Hence Node.js is the only environment that lack `DOMMatrix` support, which probably isn't that surprising given that it's browser functionality.
While the `DOMMatrix` polyfill isn't that large, it nonetheless seems completely unnecessary to bundle it in the `legacy` builds when it's not needed in browsers. However, we can avoid that by simply listing `dommatrix` as a dependency for the `pdfjs-dist` library.
