AWS Lambda for implementing static site with using S3 and CloudFront.

index.js

const path = require('path');

exports.handler = (event, context, callback) => {
    const request = event.Records[0].cf.request;
    if (!path.extname(request.uri)) {
        if (!request.uri.endsWith('/')) {
            request.uri += '/';
        }
        request.uri += 'index.html';
    }
    callback(null, request);
};