DynamoDB trigger that inserts a new record into a table called alerts if 3 or more records received in source table

sigfoxAlert.js

console.log('Loading function');

var AWS = require("aws-sdk");
var docClient = new AWS.DynamoDB.DocumentClient();

exports.handler = (event, context, callback) => {
    console.log('Received event:', JSON.stringify(event, null, 2));
    event.Records.forEach((record) => {
        console.log('Stream record: ', JSON.stringify(record, null, 2));
        console.log(record.eventID);
        console.log(record.eventName);
        console.log('DynamoDB Record: %j', record.dynamodb);
        
        if (record.eventName == 'INSERT') {
            //console.log('trigger for deviceId=', record.dynamodb.NewImage.deviceId.S);
            var deviceId = JSON.stringify(record.dynamodb.NewImage.deviceId.S);
            //console.log('trigger for deviceId=', record.dynamodb.NewImage.time.S - 300);
            var startTime = JSON.stringify(record.dynamodb.NewImage.time.S - 300);
            
            console.log('Querying for readings from ', deviceId + ": " + startTime);
    
            var params = {
                TableName : "2BEE53",
                KeyConditionExpression: "deviceId = :dev and #ti > :start",
                ExpressionAttributeNames:{
                    "#ti": "time"
                },
                ExpressionAttributeValues: {
                    ":dev": record.dynamodb.NewImage.deviceId.S,
                    ":start": startTime
                }
            };
            
            docClient.query(params, function(err, data) {
                if (err) {
                    console.error("Unable to query. Error:", JSON.stringify(err, null, 2));
                } else {
                    console.log("Query succeeded.");
                    console.log('Records returned from trigger query=', data.Count);
                    data.Items.forEach(function(item) {
                        console.log(" -", item.deviceId + ": " + item.time);
                    });
                    if (data.Count >= 3) {
                        var params2 = {
                            TableName: "alerts",
                            Item:{
                                "deviceId": record.dynamodb.NewImage.deviceId.S,
                                "time": record.dynamodb.NewImage.time.S,
                                "alertType": "movementAlert",
                                "acknowledged": "false"
                            }
                        };
                        console.log("Adding a new alert item...");
                        docClient.put(params2, function(err2, data2) {
                            if (err2) {
                                console.error("Unable to add alert. Error JSON:", JSON.stringify(err2, null, 2));
                            } else {
                                console.log("Added alert:", JSON.stringify(data2, null, 2));
                            }
                        });
                    }
                }
            });
        }
    });
    callback(null, `Successfully processed ${event.Records.length} records.`);
};