AWS billing post to SNS

index.js

const aws = require('aws-sdk');
const cw = new aws.CloudWatch({region: 'us-east-1'});
const sns = new aws.SNS();

exports.handler = (event) => {
    const endTime = new Date();
    const startTime = new Date();
    startTime.setDate(endTime.getDate() - 2); // 2 days ago
    const param = {
        MetricName: 'EstimatedCharges',
        Namespace: 'AWS/Billing',
        Period: 86400,
        StartTime: startTime,
        EndTime: endTime,
        Statistics: ['Maximum'],
        Dimensions: [
            {
                Name: 'Currency',
                Value: 'USD'
            }
        ]
    };
    cw.getMetricStatistics(param, (err, data) => {
        console.log(err, data);
        if (err) {
            console.log(err);
            return;
        }
        const dp = data["Datapoints"].sort((a, b) => {
            return (a.Timestamp < b.Timestamp) ? 1 : -1;
        });
        const prev = dp[0]["Maximum"];
        const curr = dp[1]["Maximum"];
        const diff = curr > prev ? Math.round((curr - prev)*100)/100 : curr;
        const name = process.env.ACCOUNT_NAME || "";
        const subject = `${name} Billing estimated charges ${curr} (+${diff}) USD at ${endTime.toISOString()}`;
        console.log(subject);
        const params = {
            Subject: subject,
            Message: JSON.stringify(data),
            TopicArn: process.env.SNS_TOPIC_ARN,
        };
        sns.publish(params, (err, data) => {
            if (err) {
                console.log(err);
            } else {
                console.log("success publish to SNS topic");
            }
        });
    });
};