Prior to PR 11601, the `disableCreateObjectURL` option was present on `getDocument` in the API, since it was (potentially) used when decoding JPEG images natively in the browser. Hence setting this option, which was done automatically using compatibility-code, were in some browsers necessary in order for e.g. JPEG images to be correctly rendered.
The downside of the `disableCreateObjectURL` option is that memory usage increases significantly, since we're forced to build and use `data:` URIs (rather than `blob:` URLs).
However, at this point in time the `disableCreateObjectURL` option is only necessary for *some* (non-essential) functionality in the default viewer; in particular:
- The openfile functionality, used only when manually opening a new file in the default viewer.
- The download functionality, used when downloading either the PDF document itself or its attached files (if such exists).
- The print functionality, in the generic `PDFPrintService` implementation.
Hence neither the general PDF.js library, nor the *basic* functionality of the default viewer, depends on the `disableCreateObjectURL` option any more; which is why I'm thus proposing that we remove the option since using it is a performance footgun.
*Please note:* To not outright break currently "supported" browsers, which lack proper `URL.createObjectURL` support, this patch purposely keeps the compatibility-code to explicitly disable `URL.createObjectURL` usage *only* for browsers which are known to not work correctly.[1]
While it's certainly possible that there's additional, likely older, browsers with broken `URL.createObjectURL` support, the last time that these types of problems were reported was over *three* years ago.[2]
Hence in the *very* unlikely event that additional problems occur, as a result of these changes, we can either add a new case in the compatibility-code or simply declare the affected browser as unsupported.
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[1] Which are IE11 (see issue 3977), and Google Chrome on iOS (see PR 8081).
[2] Given that `URL.createObjectURL` is used by default, you'd really expect more reports if these problems were widespread.
With the changes in previous patches, the `disableCreateObjectURL` option/functionality is no longer used for anything in the API and/or in the Worker code.
Note however that there's some functionality, mainly related to file loading/downloading, in the GENERIC version of the default viewer which still depends on this option.
Hence the `disableCreateObjectURL` option (and related compatibility code) is moved into the viewer, see e.g. `web/app_options.js`, such that it's still available in the default viewer.
Please find additional details about the ESLint rule at https://eslint.org/docs/rules/prefer-const
Note that this patch is generated automatically, by using the ESLint `--fix` argument, and will thus require some additional clean-up (which is done separately).
Note that Prettier, purposely, has only limited [configuration options](https://prettier.io/docs/en/options.html). The configuration file is based on [the one in `mozilla central`](https://searchfox.org/mozilla-central/source/.prettierrc) with just a few additions (to avoid future breakage if the defaults ever changes).
Prettier is being used for a couple of reasons:
- To be consistent with `mozilla-central`, where Prettier is already in use across the tree.
- To ensure a *consistent* coding style everywhere, which is automatically enforced during linting (since Prettier is used as an ESLint plugin). This thus ends "all" formatting disussions once and for all, removing the need for review comments on most stylistic matters.
Many ESLint options are now redundant, and I've tried my best to remove all the now unnecessary options (but I may have missed some).
Note also that since Prettier considers the `printWidth` option as a guide, rather than a hard rule, this patch resorts to a small hack in the ESLint config to ensure that *comments* won't become too long.
*Please note:* This patch is generated automatically, by appending the `--fix` argument to the ESLint call used in the `gulp lint` task. It will thus require some additional clean-up, which will be done in a *separate* commit.
(On a more personal note, I'll readily admit that some of the changes Prettier makes are *extremely* ugly. However, in the name of consistency we'll probably have to live with that.)
This moves/exposes the `URL` polyfill similarily to the existing `ReadableStream` polyfill, rather than exposing it globally, to avoid interfering with any "outside" code.
Both the `URL` and `ReadableStream` polyfills are now exposed on the `pdfjsLib` object, such that they are accessible to the viewer components.
Furthermore, the `no-restricted-globals` ESLint rule is also enabled to prevent accidental usage of the native `URL`/`ReadableStream` implementations directly in the `src/` and `web/` folders; see also https://eslint.org/docs/rules/no-restricted-globals
Addresses the remaining TODO in https://github.com/mozilla/pdf.js/projects/6
This rule is available from https://www.npmjs.com/package/eslint-plugin-mozilla, and is enforced in mozilla-central. Note that we have the necessary `Array`/`String` polyfills and that most cases have already been fixed, see PRs 9032 and 9434.
This rule is available from https://www.npmjs.com/package/eslint-plugin-mozilla, and is enforced in mozilla-central. Note that we have a polyfill for `ChildNode.remove()` and that most cases have already been fixed, see PRs 8056 and 8138.
In the first commit in PR 8203, I changed how the `DownloadManager` was included/initialized in `GENERIC`/`CHROME` builds.
The change was prompted by the fact that you cannot have conditional `import`s with ES6 modules, and I wanted to avoid bundling the general `DownloadManager` into the various Firefox specific build targets.
What I completely missed though, is that the new code meant that `download_manager.js` will now be pulling in the *entire* viewer (through `app.js`).
This is a *really* stupid mistake on my part, since it causes the `dist/build/pdf_viewer.js` used with the viewer components to now include basically the entire default viewer.
The simplest solution that I could come up with, is to add a `genericcom.js` file (similar to the `firefoxcom.js`/`chromecom.js` files) which will be responsible for importing/initializing the `DownloadManager`.
Note that as discussed on IRC, this makes the viewer slightly slower to load *only* in `gulp server` mode, however the difference seem slight enough that I think it will be fine.
The download button in pdf.js doesn't work in iOS Chrome.
- It appears to be an issue with URLs from URL.createObjectURL.
The URL is correct, but iOS Chrome won't even load the URL
when `a.click()` is called in `download_manager.js`. Even
if you manually visit the URL, you get a blank page.
- Fix this by detecting iOS Chrome and disabling createObjectURL.
The `download_manager.js` `download` method wasn't checking
`PDFJS.disableCreateObjectURL`, so check it there, too.
- Move the navigator.msSaveBlob check earlier, so that
this doesn't change IE10 / IE11 behavior.
- Remove the !URL check since pdf.js has a URL polyfill
now.
*Please note that most of the necessary code adjustments were made in PR 7890.*
ESLint has a number of advantageous properties, compared to JSHint. Among those are:
- The ability to find subtle bugs, thanks to more rules (e.g. PR 7881).
- Much more customizable in general, and many rules allow fine-tuned behaviour rather than the just the on/off rules in JSHint.
- Many more rules that can help developers avoid bugs, and a lot of rules that can be used to enforce a consistent coding style. The latter should be particularily useful for new contributors (and reduce the amount of stylistic review comments necessary).
- The ability to easily specify exactly what rules to use/not to use, as opposed to JSHint which has a default set. *Note:* in future JSHint version some of the rules we depend on will be removed, according to warnings in http://jshint.com/docs/options/, so we wouldn't be able to update without losing lint coverage.
- More easily disable one, or more, rules temporarily. In JSHint this requires using a numeric code, which isn't very user friendly, whereas in ESLint the rule name is simply used instead.
By default there's no rules enabled in ESLint, but there are some default rule sets available. However, to prevent linting failures if we update ESLint in the future, it seemed easier to just explicitly specify what rules we want.
Obviously this makes the ESLint config file somewhat bigger than the old JSHint config file, but given how rarely that one has been updated over the years I don't think that matters too much.
I've tried, to the best of my ability, to ensure that we enable the same rules for ESLint that we had for JSHint. Furthermore, I've also enabled a number of rules that seemed to make sense, both to catch possible errors *and* various style guide violations.
Despite the ESLint README claiming that it's slower that JSHint, https://github.com/eslint/eslint#how-does-eslint-performance-compare-to-jshint, locally this patch actually reduces the runtime for `gulp` lint (by approximately 20-25%).
A couple of stylistic rules that would have been nice to enable, but where our code currently differs to much to make it feasible:
- `comma-dangle`, controls trailing commas in Objects and Arrays (among others).
- `object-curly-spacing`, controls spacing inside of Objects.
- `spaced-comment`, used to enforce spaces after `//` and `/*. (This is made difficult by the fact that there's still some usage of the old preprocessor left.)
Rules that I indend to look into possibly enabling in follow-ups, if it seems to make sense: `no-else-return`, `no-lonely-if`, `brace-style` with the `allowSingleLine` parameter removed.
Useful links:
- http://eslint.org/docs/user-guide/configuring
- http://eslint.org/docs/rules/
