JSFiddle - React, Tailwind, and code Playground

JavaScript

var xml='<xml> <word> <threeletter>rip</threeletter> <fourletter>Pier</fourletter> <fiveletter>Spire</fiveletter> <sixletter>Spider</sixletter> </word> <word> <threeletter>rip</threeletter> <fourletter>Pier</fourletter> <fiveletter>Spire</fiveletter> <sixletter>Spider</sixletter> </word> <word> <threeletter>rip</threeletter> <fourletter>Pier</fourletter> <fiveletter>Spire</fiveletter> <sixletter>Spider</sixletter> </word> </xml> ';


var words={ threeletter:[], fourletter:[], fiveletter:[], sixletter:[]};
var xmlItems=['threeletter','fourletter', 'fiveletter', 'sixletter'];

$(xml).find('word').each(function(){
    var $word=$(this);
    $.each( xmlItems, function(i, item){
        words[item].push( $word.find( item ).text());
    });    
});
    
console.log(words)