async function _prepareDetails(activityId, dealId) {

var offerInfo;
var details = [];


client.connect(function(err) {
    assert.equal(null, err);
    console.log("Connected correctly to server");

    const db = client.db(dbName);
    const offers_collection = db.collection('collection_name');

    await offers_collection.aggregate([
        { "$match": { 'id': Id} },
    ]).toArray(function(err, docs) {
        assert.equal(err, null);
        console.log("Found the following records");
        details = docs;
    });
})
return details;
}

app.post('/getDetails',(request,response)=>{

var Id = request.body.Id;
var activityId = request.body.activityId;
_prepareDetails(activityId,Id).then(xx => console.log(xx));
response.send('xx');
})

function _prepareDetails(activityId, dealId) {

var offerInfo;
var details = [];


client.connect(async (err) => {
    assert.equal(null, err);
    console.log("Connected correctly to server");

    const db = client.db(dbName);
    const offers_collection = db.collection('collection_name');

    await offers_collection.aggregate([
        { "$match": { 'id': Id} },
    ]).toArray(function(err, docs) {
        assert.equal(err, null);
        console.log("Found the following records");
        details = docs;
    });
})
return details;
}