Finds all descendant elements of this document that match the specified group of selectors.
Unless your webpage contains multiple documents, the top-level querySelectorAll method behaves the same as this method, so you should use it instead to save typing a few characters.
selectors should be a string using CSS selector syntax.
var items = document.querySelectorAll('.itemClassName');
For details about CSS selector syntax, see the CSS selector specification.
Source
ElementList<Element> querySelectorAll(String selectors) {
return new _FrozenElementList._wrap(_querySelectorAll(selectors));
}