https://www.npmjs.com/package/pngjs#browser:

The package has been build with a Browserify version (npm run browserify) and you can use the browser version by including in your code:

import { PNG } from 'pngjs/browser';

In typescript you currently have to

// @ts-ignore
import { PNG as BrowserPNG } from 'pngjs/browser';
import { PNG } from 'pngjs';

const png: PNG = new BrowserPNG()