You need to place ID somewhere, so eg. add data-worksheet-id on textarea:
<textarea
data-worksheet-id="{{ $ws->id }}"
class="form-controll"
rows="4"
cols="70"
name="task"
id="{{ "updateWorksheetdonetext".$loop->index }}"
placeholder="Link til ..... !!"
>{{$ws->doneText}}</textarea>
Then get this info from tiny MC instance by:
function saveagreement (inst){
var _token = $('input[name="_token"]').val();
var doneText = tinyMCE.activeEditor.getContent();
var worksheetId = inst.getElement().dataset.worksheetId;
}
However I belive you need to alter init_instance_callback to pass editor variable:
saveagreement(e, editor);
and then in saveagreement:
function saveagreement (inst, editor){
var worksheetId = editor.getElement().dataset.worksheetId;
}