MAMA: Event-handler attributes

By Brian Wilson

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Index:

1. Introduction
2. Mouse events
3. Key events
4. Page-loading events
5. Forms-related events
6. Other popular event handlers

Introduction

Event-handler attributes are a non-portable way to directly associate Script code with a specific element via an action on that element. Event handlers were detected ~2/3 of all the URLs using Script, so a closer look at the many attributes this encompasses is useful in our discussion. MAMA's global list of markup attributes revealed 52 unique event handler attribute names, but to simplify things we will cover only the 24 that were detected more than 500 times each in MAMA's URLs. This attribute list documents over 300 element/event handler combinations; however, since the lower bound for the entire list was 50, there are surely many more element/event combinations that could be mined from MAMA.

Event handlers that occurred below the 500 threshold included the following attributes:
Onabort, Onactivate, Onafterprint, Onbeforeactivate, Onbeforecopy, Onbeforeprint, Oncontext, Ondrag, Ondraggesture, Ondrop, Onenter, Onfocusin, Onfocusout, Onhelp, Oninput, Onpropertychange, Onstart, Onmouseenter, Onmouseleave, Onmouseoff, Onmousewheel, Onmove, Onpaste, Onreset, Onselect, Onsrc, Onstart.

Mouse events

Except for a few cases, the mouse-event-handler attributes (Onmouseover, Onmouseout, Onmousedown, Onmouseup, Onmousemove, Onclick, Ondblclick and Oncontextmenu) show their greatest affinity toward the A element. The popularity and order of elements for Onmouseover and Onmouseout is quite similar, although Onmouseover enjoys a slight lead in every single case. The same can be said of another event pair—Onmousedown is slightly more popular in (almost) every element case compared to the Onmouseup attribute. The mouse event handlers were found in 1,394,783 of the URLs that MAMA analyzed, but their analogs in the DOM were only detected in 553,008 cases—the preference for the event handler version seems rather lopsided.

Onmouseover attribute

Onmouseout attribute

Onmousedown attribute

Onmouseup attribute

Onmousemove attribute

Onclick attribute

Ondblclick attribute

Oncontextmenu attribute

Key events

The Key events (Onkeypress, Onkeydown, Onkeyup) register actions taken using a keyboard. 48,825 of MAMA's URLs used at least one of these event attributes. MAMA's Script tokenization effort revealed that these events are mentioned directly in Script 68,656 times, so authors seem less inclined to use the event handler versions in this case. These event handlers are primarily used with the INPUT element, but authors use them sporadically with other elements as well. Other than the INPUT element, the different types of key activation (up/down/press) do not show any significant use patterns—the frequency rates and the elements they apply to seem to be rather haphazard.

Page-loading events

These events (Onload, Onunload and Onbeforeunload) trigger at the beginning or end of the page load process. Script logic often relies on having all of a page and its resources parsed and available to the script, so the overwhelming popularity of the Onload event use is understandable (especially its dominance on the BODY element). Authors seem to prefer the event-handler version of detecting the page loading events over using the equivalent DOM event-detection mechanism—the event-handler version was detected in 782,776 cases whereas MAMA detected only 699,741 cases using the DOM onload and onunload tokens. The overlap between the event handlers and DOM version was fairly low; only 138,585 cases used both. This means that 1,343,932 cases tried to do something with the onload event—over half of all URLs using Script in some form!

Forms-related events

While some of these event handlers are also used by other elements (like hyperlinks and BODY), these attributes see their primary usage with Forms-related elements. For the events that share element usage (Blur and Focus), the Focus attribute always seems to have considerably higher rates. Authors show a strong preference in using the Onchange event handler with the SELECT element (almost 25 times as often as INPUT), even though the use cases for both are equally interesting. Overall, these attributes were used in 430,964 URLs. The DOM methods of specifying these same events were only used in 107,824 URLs, which suggests that authors prefer to use the event-handler versions for these events.

Change, Focus, and Blur events

Onsubmit attribute

The Onsubmit event handler clocks in with very high numbers on the FORM element, and even has a respectable number of URLs using the attribute improperly with the INPUT element. This illegal INPUT[Onsubmit] usage registers considerably higher than the miserable showing (only 200 URLs) of the Onreset event handler in its valid pairing with the FORM element.

Other popular event handlers

These are the other element/event-handler combinations that registered above our arbitrary usage threshold of 500 URL cases. Most of these tend to be used with the BODY element. Applying an event handler to the BODY element usually indicates an author's desire to have the event be global in scope, so this prominence is expected.

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