The NonDocumentTypeChildNode.nextElementSibling read-only property returns the element immediately following the specified one in its parent's children list, or null if the specified element is the last one in the list.

API DOM NonDocumentTypeChildNode Property

The NonDocumentTypeChildNode.previousElementSibling read-only property returns the Element immediately prior to the specified one in its parent's children list, or null if the specified element is the first one in the list.

API DOM NonDocumentTypeChildNode Property Read-only Reference Référence