Google Analytics API

Create a Google Service Account

Go to Google Developer Console and create a new project if you haven't already.
On the sidebar click on Credentials and then Create Credentials
Select Service Account as type of credential.
Go back to the Credentials page and select Service Accounts
Select Keys tab and then Add Key then create a JSON key
Download and keep this JSON key safe.

Enable Google Analytics Data Api

On the sidebar click on APIs & Services and ENABLE APIS AND SERVICES
Search for Google Analytics Data API and enable it
Go to Analytics dashboard and click on Admin -> Property User Management -> Add Users
Add your service account email address (look in the JSON key for the email) and give it Read and Analyze access.

Install the @google-analytics/data package

Terminal

# If you're using npm
npm install @google-analytics/data

# If you're using yarn
yarn add @google-analytics/data

Set the client_email, client_id and private_key as env variables in your .env.local file

Get the Data

api/stats/index.js


import { BetaAnalyticsDataClient } from '@google-analytics/data';

export default async function handler(req, res) {

  const analyticsDataClient = new BetaAnalyticsDataClient({
    credentials: {
      client_email: process.env.ANALYTICS_CLIENT_EMAIL,
      private_key: process.env.ANALYTICS_PRIVATE_KEY.replace(/\\n/g, '\n')
    },
    projectId: process.env.ANALYTICS_PROJECT_ID
  });

  const propertyId = PROPERTY_ID; // place your property id here available in analytics console.
  let today = new Date().getTime() - 60 * 60 * 24 * 60 * 1000;
  let day = new Date(today).getDate();
  let month = new Date(today).getMonth() + 1;
  let year = new Date(today).getFullYear();

  let dayFormat = `${year}-${month}-${day}`;

  const totalReport = await analyticsDataClient.runReport({
    property: 'properties/' + propertyId,
    dateRanges: [
      {
        startDate: dayFormat,
        endDate: 'today'
      }
    ],

    metrics: [
      {
        name: 'screenpageViews'
      },
      {
        name: 'engagementRate'
      },
      {
        name: 'totalUsers'
      }
    ]
  });

  return res.status(200).json({
    pageViews: totalReport[0].rows[0].metricValues[0].value,
    engagmentRate: totalReport[0].rows[0].metricValues[1].value,
    totalUsers: totalReport[0].rows[0].metricValues[2].value
  });
}