Hi Hemant,
You can attach event handlers, say using jQuery, in your own JavaScript, like you would for any web page, and there is no particular "support" (or need thereof) in Orbeon Forms for that.
However, if you're writing XForms "by hand" (instead of creating form with Form Builder), you might want to consider using XForms events instead, like DOMActivate to handle the click on an <xf:trigger>.
Alex
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