Using the component ID as widgetVar name

jsf primefaces widget variable-names
Cold picture Cold · Sep 30, 2013 · Viewed 8.3k times · Source

I have a simple question about component IDs and dialog (or other components) widget variable name.

Is there a problem of using the component ID as widget variable name of the same component?

E.g.

<p:dialog id="dlgRelConsultasRealizadas" widgetVar="dlgRelConsultasRealizadas" .../>

Answer

BalusC picture BalusC · Sep 30, 2013

This piece of JSF generates basically the following HTML (not exactly that, but in effects the same):

<body>
    <div id="dlgRelConsultasRealizadas">...</div> <!-- Component ID -->
    <script>var dlgRelConsultasRealizadas = ...;</script> <!-- Widget var -->
</body>

Interner Explorer has problems with this approach. For some unclear reason, it pollutes the global JavaScript namespace with variable references to all HTML elements by their ID (and name). So, basically, the var dlgRelConsultasRealizadas from the generated HTML output is after the rendering been overridden by the HTML element reference on the <div>. It's like as if the browser is afterwards doing the following in the global scope:

dlgRelConsultasRealizadas = document.getElementById("dlgRelConsultasRealizadas");

This will cause all original widget var functions to be completely unavailable because the variable dlgRelConsultasRealizadas is now referencing a HTMLDivElement instance which doesn't have the same functions as the original widget var like show(), etc.

Therefore, it's recommended to give the widgetVar an unique value which is not been used as ID or name of any (generated) HTML element. A common practice is to prefix (or suffix) the widget variable name with a consistent label. E.g. the w_.

<p:dialog id="dlgRelConsultasRealizadas" widgetVar="w_dlgRelConsultasRealizadas" .../>

Update: since PrimeFaces 4.0, for among others the above reason and also because "global namespace pollution" by "3rd party libraries" is considered bad practice in JavaScript world, widget variables are not anymore injected in the global scope. They are since PF4 only available via the PF() function.

In other words, 

<p:xxx ... widgetVar="foo">

is now not available anymore as foo, but only as PF('foo'). See also Hatam Alimam's blog on the subject: Intro to PrimeFaces widgetVar.

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