Run results for: deep querySelector vs js iteration vs firstChild

Run details:

User agent: Mozilla/5.0 (Android 14; Mobile; rv:135.0) Gecko/135.0 Firefox/135.0

Browser: Firefox Mobile 135

Operating system: Android

Device Platform: Mobile

Date tested: one year ago

Test name	Executions per second
querySelector deep	63933.3 Ops/sec
while children	29525.3 Ops/sec
while firstChild	51301.2 Ops/sec

Script Preparation code:

  var levels = [document.createElement("audio"), document.createElement("span")];
  levels[1].appendChild(levels[0]);

  function getClone(depth) {
    while (depth > levels.length) {
      var span = document.createElement("span");//todo assumes that span is the simplest element for the browser to initiate.
      span.appendChild(levels[levels.length - 1]);
      levels.push(span);
    }
    return levels[depth - 1].cloneNode(true);
  }
getClone(100);

Tests:

querySelector deep
var top = getClone(10); var audio = top.querySelector("audio");
while children
var top = getClone(10); var audio = top; while(audio.children[0]) audio = audio.children[0];
while firstChild
var top = getClone(10); var audio = top; while(audio.firstChild) audio = audio.firstChild

Run results for: deep querySelector vs js iteration vs firstChild

querySelector deep

while children

while firstChild