html

<div></div>

css

@layer layerName, layerName2;

@layer layerName3 {
  div {
    font-family: serif;
  }
}

js

const item = document.getElementsByTagName("div")[0];
const rules = document.styleSheets[1].cssRules;
// Note that stylesheet #1 is the stylesheet associated with this embedded example,
// while stylesheet #0 is the stylesheet associated with the whole MDN page

const layerStatementRule = rules[0]; // A CSSLayerStatementRule
const layerBlockRule = rules[1]; // A CSSLayerBlockRule; no nameList property.

item.textContent = `@layer declares the following layers: ${layer.nameList.join(
  ", ",
)}.`;