Edit in JSFiddle

var src = 'aaaaaaabbbbbxxxxxxdddddeeezzzzzfffffffffxxxxxxxxxunko';

var rule = /[x|z]+/g;

var copy = src;
var res = [];
src.match(rule).forEach(function(m) {
    var i = copy.indexOf(m);
    if (i != 0) res.push(copy.slice(0, i-1)); // マッチじゃない部分をpush
    res.push(copy.slice(i, i+m.length)); // マッチな部分をpush
    copy = copy.slice(i+m.length); // pushした部分を削る
});
if (copy.length != 0) res.push(copy); // ケツに残りカスがあればpush
console.log(res);

document.getElementById('result').innerHTML = res;

<pre id="result"></pre>