Add a target using an Amazon SDK

    public static void putCWTargets(CloudWatchEventsClient cwe, String ruleName, String functionArn, String targetId ) {

        try {
            Target target = Target.builder()
                .arn(functionArn)
                .id(targetId)
                .build();

            PutTargetsRequest request = PutTargetsRequest.builder()
                .targets(target)
                .rule(ruleName)
                .build();

            cwe.putTargets(request);
            System.out.printf(
                "Successfully created CloudWatch events target for rule %s",
                ruleName);

        } catch (CloudWatchException e) {
            System.err.println(e.awsErrorDetails().errorMessage());
            System.exit(1);
        }
    }

Create the client in a separate module and export it.

import { CloudWatchEventsClient } from "@aws-sdk/client-cloudwatch-events";
import { DEFAULT_REGION } from "libs/utils/util-aws-sdk.js";

export const client = new CloudWatchEventsClient({ region: DEFAULT_REGION });

Import the SDK and client modules and call the API.

import { PutTargetsCommand } from "@aws-sdk/client-cloudwatch-events";
import { client } from "../libs/client.js";

const run = async () => {
  const command = new PutTargetsCommand({
    // The name of the Amazon CloudWatch Events rule.
    Rule: process.env.CLOUDWATCH_EVENTS_RULE,

    // The targets to add to the rule.
    Targets: [
      {
        Arn: process.env.CLOUDWATCH_EVENTS_TARGET_ARN,
        // The ID of the target. Choose a unique ID for each target.
        Id: process.env.CLOUDWATCH_EVENTS_TARGET_ID,
      },
    ],
  });

  try {
    return await client.send(command);
  } catch (err) {
    console.error(err);
  }
};

export default run();

// Load the AWS SDK for Node.js
var AWS = require('aws-sdk');
// Set the region 
AWS.config.update({region: 'REGION'});

// Create CloudWatchEvents service object
var cwevents = new AWS.CloudWatchEvents({apiVersion: '2015-10-07'});

var params = {
  Rule: 'DEMO_EVENT',
  Targets: [
    {
      Arn: 'LAMBDA_FUNCTION_ARN',
      Id: 'myCloudWatchEventsTarget',
    }
  ]
};

cwevents.putTargets(params, function(err, data) {
  if (err) {
    console.log("Error", err);
  } else {
    console.log("Success", data);
  }
});