forum-276.js

(function() {

    var myEditor = new YAHOO.widget.Editor('foo', {
        //Your Config
    });

    myEditor.on('afterNodeChange', function() {
	    if (this._hasSelection()) { 
	        this.toolbar.enableButton('mybutton'); 
	    } else { 
	        this.toolbar.disableButton('mybutton'); 
	    } 
	}, myEditor, true); 
    

})();