templates/sync-function/template.js
function simpleTypeFilter(doc, oldDoc, candidateDocType) {
    if (oldDoc) {
      if (doc._deleted) {
        return oldDoc.type === candidateDocType;
      } else {
        return doc.type === oldDoc.type && oldDoc.type === candidateDocType;
      }
    } else {
      return doc.type === candidateDocType;
    }
  }
function simpleTypeFilter(doc, oldDoc, candidateDocType) {
    if (oldDoc) {
      if (doc._deleted) {
        return oldDoc.type === candidateDocType;
      } else {
        return doc.type === oldDoc.type && oldDoc.type === candidateDocType;
      }
    } else {
      return doc.type === candidateDocType;
    }
  }
A type filter that matches on the document's type property