The read-only layerName property of the CSSImportRule interface returns the name of the cascade layer created by the @import at-rule.

If the created layer is anonymous, the string is empty (""), if no layer has been created, it is the null object.

A string, that can be empty, or the null object.

The document's single stylesheet contains three @import rules. The first declaration imports a stylesheet into a named layer. The second declaration imports a stylesheet into an anonymous layer. The third declaration imports a stylesheet without a layer declaration.

The layerName property returns the name of the layer associated with the imported stylesheet.

@import url("style1.css") layer(layer-1);
@import url("style2.css") layer;
@import url("style3.css");

const myRules = document.styleSheets[0].cssRules;
console.log(myRules[0].layerName); // returns `"layer-1"`
console.log(myRules[1].layerName); // returns `""` (an anonymous layer)
console.log(myRules[2].layerName); // returns `null`

• Learning area : Cascade layers
• @import and @layer