Range.endOffset

The Range.endOffset read-only property returns a number representing where in the Range.endContainer the Range ends.

If the endContainer is a Node of type Text, Comment, or CDATASection, then the offset is the number of characters from the start of the endContainer to the boundary point of the Range. For other Node types, the endOffset is the number of child nodes between the start of the endContainer and the boundary point of the Range. This property is read-only. To change the endOffset of a Range, use one of the Range.setEnd methods.

const range = document.createRange();

range.setStart(startNode,startOffset);
range.setEnd(endNode,endOffset);
endRangeOffset = range.endOffset;