One of the patches in https://bugzilla.mozilla.org/show_bug.cgi?id=1202902, specifically [`Mass replace toplevel 'let' with 'var' in preparation for global lexical scope. (rs=jorendorff)`](https://hg.mozilla.org/mozilla-central/rev/380817d573cd), touches PDF.js code. Unfortunately it was landed upstream without, as far as I can tell, notifying us about it.
This patch uplifts the relevant changes to avoid future merge conflicts, and for consistency also tweaks `PdfJs-stub.jsm`.
When the user edits the URL and changes the reference fragment (hash),
PDF.js intercepts this action, and saves the then-current history state
in the previous history entry. This is implemented by navigating back,
editing the history and navigating forward again.
The current logic has a flaw: It assumes that calling history.back() and
history.forward() immediately updates the history state. This is however
not guaranteed by the web standards, which states that calling e.g.
history.back "must traverse the history by a delta -1", which means that
the browser must QUEUE a task to traverse the session history, per spec:
http://w3.org/TR/2011/WD-html5-20110113/history.html#dom-history-backhttps://html.spec.whatwg.org/multipage/browsers.html#dom-history-back
Firefox and Internet Explorer deviate from the standards by immediately
changing the history state instead of queuing the navigation.
WebKit derived browsers (Chrome, Opera, Safari) and Opera presto do not.
The user-visible consequence of strictly adhering to the standards in
PDF.js can be shown as follows:
1. Edit the URL.
2. Append #page=2 for example.
3. Press Enter.
-> Presto and WebKit: PDF.js reverts to the previous URL.
-> Gecko and Trident: PDF.js keeps the new URL, as expected.
To fix the issue, modification of the previous history item happens in
a few asynchronous steps, guided by the popstate event to detect when
the history navigation request has been committed.
--
Some more implementation notes:
I have removed the preventDefault and stopPropagation calls, because
popstate is not cancelable, and window is already the last target of the
event propagation.
The previous allowHashChange logic was hard to follow, because it did
not explain that hashchange will be called twice; once during the
popstate handler for history.back() (which will reset allowHashChange),
and again for history.forward() (where allowHashChange will be false).
The purpose of allowHashChange is now more explicit, by incorporating
the logic in the replacePreviousHistoryState helper function.
*This regressed in PR 4920.*
The main motivation for PR 4920 was to quickly get rid of old canvases when pages are evicted from the `PDFPageViewBuffer` cache. However it inadvertently broke the use-case where the `canvas` is used as a preview, on scale or rotation changes, until the re-rendering is finished.
Fixes 6467.
In PR 5552, specifically commit 9f384bbb41, the meaning of `this.annotationLayer` changed in `PDFPageView`. Previously it referred directly to a DOM element, but now it's instead an instance of `AnnotationsLayerBuilder`.
This patch tweaks things so that we won't try to hide a non-existent `annotationLayer` div in `PDFPageView_reset`, and also so that we don't attempt to insert empty (`null`) DOM elements in `PDFPageView_draw`.
The file (`lshort.pdf`) has changed a couple of times since the test was added, hence there's no guarantee that the current version accurately reflects the issues the test was added to check.
In this patch, I'm updating the link location to point to the *intended* file version (hosted on the "Internet Archive").
According to the PDF spec 5.3.2, a positive value means in horizontal,
that the next glyph is further to the left (so narrower), and in
vertical that it is further down (so wider).
This change fixes the way PDF.js has interpreted the value.
