Need to add confirm (Yes or No) prompt to javascript function

I need to update the following javascript function with a confirm dialog (ie: Yes or No prompt):

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// BetterInnerHTML v1.15 - by Craig Buckler, http://www.optimalworks.net/
function BetterInnerHTML(_1,_2,_3){function Load(_4){var _5;if(typeof DOMParser!="undefined"){_5=(new DOMParser()).parseFromString(_4,"application/xml");}else{var _6=["MSXML2.DOMDocument","MSXML.DOMDocument","Microsoft.XMLDOM"];for(var i=0;i<_6.length&&!_5;i++){try{_5=new ActiveXObject(_6[i]);_5.loadXML(_4);}catch(e){}}}return _5;}function Copy(_8,_9,_a){if(typeof _a=="undefined"){_a=1;}if(_a>1){if(_9.nodeType==1){var _b=document.createElement(_9.nodeName);for(var a=0,attr=_9.attributes.length;a<attr;a++){var _d=_9.attributes[a].name,aValue=_9.attributes[a].value,evt=(_d.substr(0,2)=="on");if(!evt){switch(_d){case "class":_b.className=aValue;break;case "for":_b.htmlFor=aValue;break;default:_b.setAttribute(_d,aValue);}}}_8=_8.appendChild(_b);if(evt){_8[_d]=function(){eval(aValue);};}}else{if(_9.nodeType==3){var _e=(_9.nodeValue?_9.nodeValue:"");var _f=_e.replace(/^\s*|\s*$/g,"");if(_f.length<7||(_f.indexOf("<!--")!=0&&_f.indexOf("-->")!=(_f.length-3))){_8.appendChild(document.createTextNode(_e));}}}}for(var i=0,j=_9.childNodes.length;i<j;i++){Copy(_8,_9.childNodes[i],_a+1);}}_2="<root>"+_2+"</root>";var _11=Load(_2);if(_1&&_11){if(_3!=false){while(_1.lastChild){_1.removeChild(_1.lastChild);}}Copy(_1,_11.documentElement);}}

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How would I do that?  Also, ... how would I update the link that triggers the function? :

<a href='javascript:BetterInnerHTML(document.getElementById("narrative"),"Text to be inserted");'>Insert</a>

Please advise.

Thanks,
- Yvan