Copying a section from Google Docs to another Doc using Apps Script

I've successfully used this code to copy the entirety of one doc into another doc:

const newestFile = DocumentApp.openById("ID").getBody();
const archive = DocumentApp.openById("ID").getBody();
let index = 12;
  let el, type;
  for (let i = 0; i < newestFile.getNumChildren(); i++){
    el = newestFile.getChild(i);
    type = el.getType();
    switch (type){
      case DocumentApp.ElementType.PARAGRAPH:
        archive.insertParagraph(index,el.copy());
        index++;
        break;
      case DocumentApp.ElementType.LIST_ITEM:
        archive.insertListItem(index,el.copy());
        index++;
        break;
      case DocumentApp.ElementType.TABLE:
        archive.insertTable(index,el.copy());
        index++;
        break;
    }
  }

However, I now need to copy a portion of a doc into another doc, and I can't figure it out. If I knew how to get the body index of any element I could do it the same way, but I don't know if that's even possible. The text I need to copy out will always be preceded by a specific text ("Current Week") and end immediatly before a specific text ("ARCHIVE").

Solution

Description

Here is a simple example of how to copy between certain text. I've only covered paragraphs and tables but any other type of Element can be handled.

Test Document

Script

function myFunction() {
  try {
    let doc = DocumentApp.getActiveDocument();
    let body = doc.getBody();
    let count = body.getNumChildren();
    doc = DocumentApp.create("dummy");
    let copy = doc.getBody();
    let start = false;

    for( let i=0; i<count; i++ ) {
      let child = body.getChild(i);
      if( child.getType() == DocumentApp.ElementType.PARAGRAPH ) {
        if( child.asParagraph().findText("Current Week") ) start = true; 
        if( start ) copy.appendParagraph(child.asParagraph().copy());
        if( child.asParagraph().findText("ARCHIVE") ) break;
      }
      else if( child.getType() == DocumentApp.ElementType.TABLE ) {
        if( start ) copy.appendTable(child.asTable().copy());
      }
      else if( child.getType() == DocumentApp.ElementType.LIST_ITEM ) {
        if( start ) {
          let listItem = child.asListItem();
          let glyphType = listItem.getGlyphType();
          listItem = copy.appendListItem(listItem.copy());
          listItem.setGlyphType(glyphType)
        }
      }
    }
  }
  catch(err) {
    console.log("Error in myFunction - "+err)
  }
}

Reference