Use of JavaScript in Fossil


The Fossil development project’s policy is to use JavaScript where it helps make its web UI better, but to offer graceful fallbacks wherever practical. The intent is that the UI be usable with JavaScript entirely disabled. In every place where Fossil uses JavaScript, it is an enhancement to provided functionality, and there is always another way to accomplish a given end without using JavaScript.

This is not to say that Fossil’s fall-backs for such cases are always as elegant and functional as a no-JS purist might wish. That is simply because the vast majority of web users run with JS enabled, and a minority of those run with some kind of conditional JavaScript blocking in place. Fossil’s active developers do not deviate from that norm enough that we have many no-JS purists among us, so the no-JS case doesn’t get as much attention as some might want. We do accept code contributions, and we are philosophically in favor of graceful fall-backs, so you are welcome to appoint yourself the position of no-JS czar for the Fossil project!

Evil is in actions, not in nouns, so we do not believe JavaScript can be evil. It is an active technology, but the actions that matter here are those of writing the code and checking it into the Fossil project repository. None of the JavaScript code in Fossil is evil, a fact we enforce by being careful about who we give check-in rights on the repository to and by policing what code does get contributed. The Fossil project does not accept non-trivial outside contributions.

We think it’s better to ask not whether Fossil requires JavaScript but whether Fossil uses JavaScript well, so that you can decide to block or allow Fossil’s use of JavaScript.

Blocking JavaScript

Rather than either block JavaScript wholesale or give up on blocking JavaScript entirely, we recommend that you use tools like NoScript or uBlock Origin to selectively block problematic uses of JavaScript so the rest of the web can use the technology productively, as it was intended. There are doubtless other useful tools of this sort; we recommend only these two due to our limited experience, not out of any wish to exclude other tools.

The primary difference between these two for our purposes is that NoScript lets you select scripts to run on a page on a case-by-case basis, whereas uBlock Origin delegates those choices to a group of motivated volunteers who maintain whitelists and blacklists to control all of this; you can then override UBO’s stock rules as needed.

How Many Users Run with JavaScript Disabled Anyway?

There are several studies that have directly measured the web audience to answer this question:

Our sense of this data is that only about 0.2% of web users had JavaScript disabled while participating in these studies.

The Fossil user community is not typical of the wider web, but if we were able to comprehensively survey our users, we’d expect to find an interesting dichotomy. Because Fossil is targeted at software developers, who in turn are more likely to be power-users, we’d expect to find Fossil users to be more in favor of some amount of JavaScript blocking than the average web user. Yet, we’d also expect to find that our user base has a disproportionately high number who run powerful conditional blocking plugins in their browsers, rather than block JS entirely. We suspect that between these two forces, the number of no-JS purists among Fossil’s user base is still a tiny minority.

No Third-Party JavaScript in Fossil

Fossil does not use any third-party JavaScript libraries, not even very common ones like jQuery. Every bit of JavaScript served by the stock version of Fossil was written specifically for the Fossil project and is stored in its code repository.

Therefore, if you want to hack on the JavaScript code served by Fossil and mechanisms like skin editing don’t suffice for your purposes, you can hack on the JavaScript in your local instance directly, just as you can hack on its C, SQL, and Tcl code. Fossil is free and open source software, under a single license.

Fossil Does Not Snoop On You

There is no tracking or other snooping technology in Fossil other than that necessary for basic security, such as IP address logging on check-ins. (This is in part why we have no comprehensive user statistics!)

Fossil attempts to set two cookies on all web clients: a login session cookie and a display preferences cookie. These cookies are restricted to the Fossil instance, so even this limited data cannot leak between Fossil instances or into other web sites.

There is some server-side event logging, but that is done entirely without JavaScript, so it’s off-topic here.

Places Where Fossil’s Web UI Uses JavaScript

The remainder of this document will explain how Fossil currently uses JavaScript and what it does when these uses are blocked.

Timeline Graph

Fossil’s web timeline uses JavaScript to render the graph connecting the visible check-ins to each other, so you can visualize parent/child relationships, merge actions, etc. We’re not sure it’s even possible to render this in static HTML, even with the aid of SVG, due to the vagaries of web layout among browser engines, screen sizes, etc.

Fossil also uses JavaScript to handle clicks on the graph nodes to allow diffs between versions, to display tooltips showing local context, etc.

Graceful Fallback: When JavaScript is disabled, this column of the timeline simply collapses to zero width. All of the information you can get from the timeline can be retrieved from Fossil in other ways not using JavaScript: the “fossil timeline” command, the “fossil info” command, by clicking around within the web UI, etc.

Potential Workaround: The timeline could be enhanced with <noscript> tags that replace the graph with a column of checkboxes that control what a series of form submit buttons do when clicked, replicating the current JS-based features of the graph using client-server round-trips. For example, you could click two of those checkboxes and then a button labeled “Diff Selected” to replicate the current “click two nodes to diff them” feature.

WYSIWYG Wiki Editor

The Admin → Wiki → “Enable WYSIWYG Wiki Editing” toggle switches the default plaintext editor for Fossil wiki documents to one that works like a basic word processor. This feature requires JavaScript in order to react to editor button clicks like the “B” button, meaning “make [selected] text boldface.” There is no standard WYSIWYG editor component in browsers, doubtless because it’s relatively straightforward to create one using JavaScript.

Graceful Fallback: Edit your wiki documents in the default plain text wiki editor. Fossil’s wiki and Markdown language processors were designed to be edited that way.

Line Numbering

When viewing source files, Fossil offers to show line numbers in some cases. Toggling them on and off is currently handled in JavaScript. (Example.)

Workaround: Edit the URL to give the “ln” query parameter per the /file docs, or provide a patch to reload the page with this parameter included/excluded to implement the toggle via a server round-trip.

Side-by-Side Diff Mode

The default “diff” view is a side-by-side mode. If either of the boxes of output — the “from” and “to” versions of the repo contents for that check-in — requires a horizontal scroll bar given the box content, font size, browser window width, etc., both boxes will usually end up needing to scroll since they should contain roughly similar content. Fossil therefore scrolls both boxes when you drag the scroll bar on one because if you want to examine part of a line scrolled out of the HTML element in one box, you probably want to examine the same point on that line in the other box.

Graceful Fallback: Manually scroll both boxes to sync their views.

Table Sorting

On pages showing a data table, the column headers may be clickable to do a client-side sort of the data on that column.

Potential Workaround: This feature could be enhanced to do the sort on the server side using a page re-load.

File Browser Tree View

The file browser’s tree view mode uses JavaScript to handle clicks on folders so they fold and unfold without needing to reload the entire page.

Graceful Fallback: When JavaScript is disabled, clicks on folders reload the page showing the folder contents instead. You then have to use the browser’s Back button to return to the higher folder level.

Version Hashes

In several places where the Fossil web UI shows a check-in hash or similar, hovering over that check-in shows a tooltip with details about the type of artifact the hash refers to and allows you to click to copy the hash to the clipboard.

Graceful Fallback: When JavaScript is disabled, these tooltips simply don’t appear. You can then select and copy the hash using your browser, make “fossil info” queries on those hashes, etc.

Anti-Bot Defenses

Fossil has anti-bot defenses, and it has some JavaScript code that, if run, can drop some of these defenses if it decides a given page was loaded on behalf of a human, rather than a bot.

Graceful Fallback: You can use Fossil’s anonymous login feature to convince the remote Fossil instance that you are not a bot. Coupled with the Fossil user capability system, you can restore all functionality that Fossil’s anti-bot defenses deny to random web clients by default.

Hamburger Menu

The default skin includes a “hamburger menu” (☰) which uses JavaScript to show a simplified version of the Fossil UI site map using an animated-in dropdown.

Graceful Fallback: Clicking the hamburger menu button with JavaScript disabled will take you to the /sitemap page instead of showing a simplified version of that page’s content in a drop-down.

Workaround: You can remove this button by editing the skin header.


Some stock Fossil skins include JavaScript-based features such as the current time of day. The Xekri skin includes this in its header, for example. A clock feature requires JavaScript not only to get the time and update inline on the page once a minute, but also so it displays in the local time zone.

Since none of this code provides a necessary Fossil feature, the core developers are unlikely to try to make these features work better in the absence of JavaScript.

However, we are willing to study patches to make this better. For example, the wall clock displays could include the page load time in the dynamically generated HTML shipped from the remote Fossil server, so that in the absence of JavaScript, you at least get the page generation time, expressed in the server’s time zone.