the answer to a question i was asked years ago, but sans jQuery

nojq.js

var tbl = document.querySelectorAll('table.someId');
var rows = Array.from(tbl.querySelectorAll('tr')).filter(function(row, idx) { return (idx % 2);});
tbl.removeChild(tbl.querySelector('tbody'));
rows.forEach(function (row) {
  tbl.appendChild(row);
});