Linebreaks within the JavaScript code leads to Syntax errors. Also PostEntries variable was referenced as postentries. Change the Javascript as follows -
<script>function LoadTheArchive(TotalFeed) { var PostTitles = new Array(); var PostURLs = new Array(); var PostYears = new Array(); var PostMonths = new Array(); var PostDays = new Array(); if("entry" in TotalFeed.feed) { var PostEntries=TotalFeed.feed.entry.length; for(var PostNum=0; PostNum<PostEntries ; PostNum++) { var ThisPost = TotalFeed.feed.entry[PostNum]; PostTitles.push(ThisPost.title.$t); PostYears.push(ThisPost.published.$t.substring(0,4)); PostMonths.push(ThisPost.published.$t.substring(5,7)); PostDays.push(ThisPost.published.$t.substring(8,10)); var ThisPostURL; for(var LinkNum=0; LinkNum < ThisPost.link.length; LinkNum++) { if(ThisPost.link[LinkNum].rel == "alternate") { ThisPostURL = ThisPost.link[LinkNum].href; break } } PostURLs.push(ThisPostURL); } } DisplaytheTOC(PostTitles,PostURLs,PostYears,PostMonths,PostDays);}function DisplaytheTOC(PostTitles,PostURLs,PostYears,PostMonths,PostDays){ var MonthNames=["Enero","Febrero","Marzo","Abril","Mayo","Junio","Julio","Agosto","Septiembre","Octubre","Noviembre","Diciembre"]; var NumberOfEntries=PostTitles.length; var currentMonth = ""; var currentYear = ""; for(var EntryNum = 0; EntryNum < NumberOfEntries; EntryNum++) { NameOfMonth = MonthNames[parseInt(PostMonths[EntryNum],10)-1] if (currentMonth != NameOfMonth || currentYear != PostYears[EntryNum]) { currentMonth = NameOfMonth; currentYear = PostYears[EntryNum]; document.write("<div class='dateStyle'><br />"+ currentMonth+""+currentYear+"</div>"); } document.write('<a href ="'+PostURLs[EntryNum]+'"><div class=dayStyle>'+parseInt(PostDays[EntryNum],10)+": </div>"+PostTitles[EntryNum]+"</a><br />"); }}</script><script src="https://tecnoriales.com/feeds/posts/default?max-results=500&alt=json-in-script&callback=LoadTheArchive" />You will notice that last 2 document.write statements have the linebreaks removed