Retrieve attribute value of html element within var string containing HTML, via jQuery
JavaScript
// This value of var selectionFromTinyMCE is an example
// of what parent.tinyMCE.activeEditor.selection.getContent(); returns to you
var selectionFromTinyMCE = 'sit our <a href="../forum/index.php">community forum</a>! We also';
// Here we take the string returned by TinyMCE, wrap it with a span tag,
// and pass it into a jQuery. This forces jQuery to evaluate the string as HTML!
var $jStr = $("<span>"+selectionFromTinyMCE+"</span>");
// You then create new variable and store the value of the href attribute
// of the <a> element from within your string.
var hrefValueFromTinyMCEselection = $jStr.find("a").attr("href");
// Check the console to see the result below, outputted as a string
console.log( hrefValueFromTinyMCEselection );