PouchDB: Add or update record (sync / merge)

pouchdb-create-or-update-merge.js

static addOrUpdate(id, document) {
    return new Promise(function (resolve, reject) {
        let doStore = function (originalDocument) {
            // Merge the document: First, set the ID. Then apply the existing doc on top if possible. Finally, apply the changed doc.
            let mergedDoc = {
                _id: id
            };

            if (originalDocument) {
                for (let key in originalDocument) {
                    mergedDoc[key] = originalDocument[key];
                }
            }

            for (let key in newDocument) {
                mergedDoc[key] = newDocument[key];
            }

            // Verify whether the merged document actually has any changed properties other than revision
            if (originalDocument) {
                let anyUnequal = false;

                for (let key in mergedDoc) {
                    if (key === "_rev") {
                        continue;
                    }

                    if (originalDocument[key] !== mergedDoc[key]) {
                        console.log('PROP NOT EQUAL', key);
                        anyUnequal = true;
                        break;
                    }
                }

                if (!anyUnequal) {
                    // All properties equal, no need to perform merge
                    resolve(mergedDoc);
                    return;
                }
            }

            // Update needed, perform put
            DeviceDb.db.put(mergedDoc).then(function (response) {
                mergedDoc._rev = response.rev;
                resolve(mergedDoc);
            })
            .catch(function (err) {
                reject(err);
            });
        };

        // Fetch the document, see what happens, then store or update
        db.get(id).then(function (getDoc) {
            // Document exists, update
            doStore(getDoc);
        }).catch(function (err) {
            if (err.status === 404) {
                // Document does not exist, create
                doStore(null);
            } else {
                // Something else went wrong, general failure
                reject(err);
            }
        });
    });
}

Example use:

ExDbClass.addOrUpdate("mydoc", { description: "changed" }).then(function (document) {
    console.log(document); // Object {_id: "mydoc", description: "new", _rev: "1-4d4874e4817ded18aa5575d74f0f1c52"}
});

And again:

ExDbClass.addOrUpdate("mydoc", { secondary: "update" }).then(function (document) {
    console.log(document); // Object {_id: "mydoc", description: "new", _rev: "2-803b42574d364351252a7564edd3f564", secondary: "update"}
});

Also, it won't create a new revision if nothing changed.