var doc = DocumentApp.getActiveDocument();
var paragraphs = doc.getBody().getParagraphs();
for (var i = 0; i < paragraphs.length; i++) {
if (paragraphs[i].getType() == DocumentApp.ElementType.PARAGRAPH) {
    var heading = paragraphs[i].asParagraph().getHeading();
    //get only headings
    if (heading == DocumentApp.ParagraphHeading.HEADING1) {
    var title = paragraphs[i].asParagraph().asText().getText();
    if (title != "") {
        //put every headings into its own range, so it has its own id
        var rangeBuilder = doc.newRange().addElement(paragraphs[i]);
        var id = doc.addNamedRange('toc', rangeBuilder.build()).getId();
        // check offset and text of the rangeElement
        var offset = doc.getNamedRangeById(id).getRange().getRangeElements()[0].getStartOffset();
        var text = doc.getNamedRangeById(id).getRange().getRangeElements()[0].getStartOffset();
    }
}

doc.setCursor(doc.newPosition(rangeElement.getElement(), rangeElement.getStartOffset()));