Table of Contents
- Modifying Object.prototype
- SVG or VML
- Console warnings and breakpoint on exceptions
- CSS Transition/Animation/Transforms
- Native Selector Bugs
- Focus and Blur Event Order
- Inline Event Handlers
- Negative margins on Android 4.0-4.3 browser
- Quirks Mode
- outerHeight() behavior for tables with captions
- Passing documentFragment to the API for manipulation or traversal
Sometimes there are issues that the jQuery core team believes can't be adequately fixed. Typically the reasons fall into one or more of these categories:
- Lack of browser APIs to detect and fix the problem;
- Conflicts--for example, fixing a bug in Browser A creates one in Browser B;
- Severe breakage to jQuery APIs are required to fix the problem;
- Serious performance implications of fixing a relatively rare problem; or
- Significant amounts of code are required to fix the problem.
The issues below are ones that have been repeatedly raised over time that the team has decided not to fix. If you have specific new ideas for a solution that have not already been considered, please open a new ticket.
Modifying Object.prototype
Modifying JavaScript's Object.prototype by adding new properties or methods has long been acknowledged as a bad idea; it'll break a lot of code, and not just in jQuery.
For further reference:
SVG or VML
jQuery is primarily intended as a library for the HTML DOM, so most problems related to SVG/VML documents are out of scope. Although XML-based markup such as SVG may look like HTML, its behavior is often very different and browsers do not support the same APIs on them. We do try to address problems that "bleed through" to HTML documents, such as events that bubble out of SVG embedded into HTML. As of jQuery 3.0 we also allow class name operations on SVG elements.
For further reference:
- trac-4208: Selector inconsistency with XML Namespaces
- trac-7584: SVG support metaticket
- trac-9807: IE7/8 alerts a 'Failed' error on VML objects
- trac-13092: vendorPropName on a namespaced element
- gh-2199: jQuery Class Operations on SVG DOM Attributes
- gh-2889: Chrome is deprecating offsetWidth and offsetHeight
Console warnings and breakpoint on exceptions
Some versions of Chrome and Firefox will generate warnings on the console when specific properties are accessed. Browsers may also throw exceptions that jQuery catches and handles. Both are part of jQuery's cross-browser feature detection. When using browser dev tools, you may encounter a breakpoint inside jQuery if you have enabled "Break on caught exceptions" but this is normal.
For further reference:
- trac-7535: Firefox Console error: Unexpected token in attribute selector
- trac-10531: Consider removing layerX and layerY from $.event.props
- trac-13881: IE10 SCRIPT5022: Caught exception occurred : SyntaxError
- gh-2889: Chrome is deprecating offsetWidth and offsetHeight
CSS Transition/Animation/Transforms
Modern browsers provide native means of doing CSS animations and transforms just by adding or removing class names. jQuery's .animate() method is best saved for more complex animations where the CSS mechanisms are insufficient. If you wish to take advantage of CSS animations through jQuery's .animate() method, we recommend a plugin.
For further reference:
Plugins available:
Native Selector Bugs
Browsers have inconsistencies with their implementations of querySelectorAll, which bleed through to jQuery. Thankfully these issues are usually fixed quickly. If they aren't that severe then we just bump them back to the browser vendor and let them handle it. We also are hesitant to "fix" cases that aren't specified by either a formal standard or (at minimum) de facto agreement by browsers.
For further reference:
- trac-9690: nth-child + class does not work in Firefox 5
- gh-2670: :target doesn't match elements on initial page load in Chrome and Firefox
Focus and Blur Event Order
The focus, blur, focusin, and focusout events occur in different orders in different browsers, and it is not practical for jQuery to impose a consistent order--especially when most browsers do not follow any standard. In addition, IE11 focus and blur events are asynchronous; the events don't fire on the same thread as where they are triggered.
For further reference:
Inline Event Handlers
In general, inline event handlers are incredibly hard to work with and should not be used. In nearly all cases, issues involving inline event handlers are out of scope. Inline handlers do not behave the same way as event handlers added with the standard DOM addEventListener method.
For further reference:
Negative margins on Android 4.0-4.3 browser
In Android 4.0-4.3, the DOM getComputedStyle() method sometimes returns percents instead of pixel values. The workaround for this bug in jQuery leads to another issue that causes the return of incorrect values when retrieving negative margins.
For further reference:
Quirks Mode
Some browsers provide a "Quirks Mode" that does not conform to the standard W3C CSS box model; jQuery does not support this mode due to the differences it introduces in measuring element dimensions and positions. To ensure that an HTML document does not render in Quirks Mode, always use a doctype at the top of the document.
For further reference:
outerHeight() behavior for tables with captions
The spec is unclear whether getComputedStyle(table).height should take table's caption into account or not. Firefox doesn't include it while Chrome does. As long as it's not clear which of those behavior is expected, we're not going to normalize in either direction.
For further reference:
Passing documentFragment to the API for manipulation or traversal
jQuery uses document fragments internally and doesn't expect them to be passed as API inputs.
For further reference: