How do I include boomerangjs script file in angular 7?

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Angular6

I am trying to implement boomerangjs in my Angular code. But it's not working for me. I need your help to resolve it. Below is the way I've used it. So first I've installed boomerangjs using npm and it's now available in my node_modules. My first page is dashboard.component.ts, so I've added below code in this component.

import {BOOMR} from 'node_modules/boomerangjs';

    export class DashboardComponent implements OnInit {
      ngOnInit() {         
         BOOMR.init({
          beacon_url: "/beacon"
        });   
        }
    }

However I am getting TypeError: Cannot read property 'init' of undefined error. Please help how can I use "boomerangjs " in my angular code.

I am able to see 3 dots ... on top of page where import is listed. When I hover on dots getting below message:

Could not find a declaration file for module 'node_modules/boomerangjs'. 'd:/code/node_modules/boomerangjs/boomerang.js' implicitly has an 'any' type.
  Try `npm install @types/boomerangjs` if it exists or add a new declaration (.d.ts) file containing `declare module 'boomerangjs';`

Please help Thanks

What I have tried:

I tried to import boomerangjs using below ways. Even I created boomerang.d.ts and referred in tsconfig.json but nothing is working for me. 

//import * as BOOMR from 'node_modules/boomerangjs';
//import  "node_modules/boomerangjs/boomerang.d.ts";
const BOOMR = require('node_modules/boomerangjs');