Skip to content

Undetectables

Jump to bottom
davidcalhoun edited this page Oct 3, 2011 · 80 revisions

The Undetectables

These things cannot be feature detected. They must rely on either:

  1. UA sniffing
  2. Browser inferences
  3. Providing the same (slow) fix to everyone

Categories of Undetectables:

HTML5

  • registerProtocolHandler() support (existed in webkit but doesnt do anything, still live in iOS/Android likely.)
  • File Drag 'n Drop (webkit doesnt expose a global DataTransfer constuctor to inspect) issue 57
  • webforms UI: datepicker, colorpicker UIs cannot be detected, only the associated constraint validation
  • inability to edit things in contenteditable/designMode in mobile Webkit browsers

Audio/Video

  • timeupdate video/audio event fires inconsistently across webkit and moz
  • HTML5 video readyState is inconsistent across webkit(4) and moz(3)
  • canPlayType() results on mobile are unreliable
  • preload attribute support, can't be tested without bandwidth-consuming tests (Chrome has implemented the preload-IDL, but not the feature)
  • loop attribute support, can't be tested without bandwidth-consuming tests (support for this attribute is practically non-existent)

Networking

  • script tag onload/onerror/onreadystatechange actual behaviour (atomicity, order, etc etc)
  • link tag / stylesheet onload actual behaviour (exists in webkit / ff but never fires)
  • Network related metrics, a la the Browserscope Networking Results (|| script, css, etc)

Typography / Text

  • ClearType disabling during opacity changes
  • FOUT behavior of Gecko's @font-face support
  • font rendering (like smoothing, anti-aliasing, font-weight diffs among browsers/platforms)
  • consistent rendering ( in the page and alert() dialogs) of HTML entities
  • proper handling of CSS text-overflow:ellipsis behavior on text
  • native spellchecking (added in ie10pp3)

Events

  • keyboard event bugs, especially related to the keydown/keypress events, and the keyCode/charCode event properties.
  • the order (and reliability) of mousedown, click, and mouseup events (especially if a mousedblclick is happening)
    • especially when fired on a form element like a checkbox, reliability of state update of the element compared to when the events fire
  • whether a scroll wheel event is coming from a continuous device like a trackpad or the Magic Mouse or from a traditional clicking scroll wheel (in webkit).
  • onhashchange is case insensitive in IE8 (maybe 9 too?), all others are case sensitive (HTML5 requires case sensitivity). Can't be detected without actually triggering a hashchange event.
  • IE8 in compatibility view mode has onhashchange, but doesn't support it. Workaround is to test for document.documentMode > 8.
  • support for DOMContentLoaded.
    • You can add an event listener and hope, fall back to document.readyState or window.onload or in IE, the doScroll technique.
  • the oninput event.
  • WebKit popstate (history API) out-of-synch issues (http://www.bcherry.net/playground/pushstate/)

CSS

  • <select> display in IE6
  • PNG alpha transparency
  • The look of the various *-resize cursors is very different across browsers and platforms.
  • IE6 css bugs like duplicate characters bug
  • IE display transparency bug on height > 4096px
  • Generated content detection is now part of Modernizr core tests see L640
    CSS Generated Content support
  • False positives for box-shadow, border-radius, etc (happens in Aurora/Midori/etc) issue 169
  • pointer-events false positive in Opera
  • position:fixed support in iOS and Android

Edge cases

  • IE CSS bug where certain types of positioning of an <input type=text> element can cause that element's autocomplete box to not render at the same location as the actual input box.
  • strange treatment of <!-- --> comment nodes in the DOM (in IE)... like in some cases, a comment node will be moved to be a child of the previous element even though it's not a child proper. Can cause things like :empty to fail differently.
  • resize event firing rate. e.g. you can't keep an element's position smoothly updated in response to resize or scroll.

General undetectables

  • Memory leaks
  • DOM/JS performance (e.g.: innerHTML vs. DOM manipulation)
    • Testable, but typically not feasible to test just to avoid code forking.
  • Hardware Acceleration
    • Whether a CSS transition can use (or did use) accelerated compositing. If an effect isn't going to be hardware-accelerated, then a setTimeout animation is often more performant than a non-accelerated CSS transition. No reliable way to measure the framerate of a CSS transition.

This might not be a complete list

Add to the list if you know more Undetectables. Likewise, link to possible solutions if you think an item listed here can be feature-detected.

Contributors: paulirish, jaubourg, rwaldron, zachleat, snover, devongovett, rgrove, savetheclocktower, getify, garann, jdalton, michaelbrundage, necolas, mislav, davidcalhoun

Clone this wiki locally