NuxtJS comes with some default polyfills, and it is recommended not to use the same ones from polyfill.io. Doing this would increase the page weight unnecessarily, affecting the page-loading performance.

Polyfills for IE11 compatibility are added by default. Along with this, polyfills for the following are also added by default:

fetch() replaces whatwg-fetch and unfetch on the client-side, and isomorphic-unfetch and node-fetch on the server-side.
URL of NodeJS is supported through URL.
object-assign, object.assign, and core-js/object/assign are supported by Object.assign()
Supports all ES6 features out of the box
NextJS also supports many features beyond ES6:
- Async/await (ES2017)
- Object rest/spread properties (ES2018)
- Dynamic import() (ES2020)
- Optional chaining (ES2020)
- Nullish coalescing (ES2020)
- Class fields and static properties (part of stage 3 proposal)
Built in Typescript support.

Bad Practice

import { Head } from "next/document";
export class Card extends Head {
  render() {
    const data = Object.assign(source, target)
    return (
      <div>
        <h1>Hello title</h1>
        <script src="https://polyfill.io/v3/polyfill.min.js?features=Object.assign"></script>
      </div>
    );
  }
}

Recommended

import { Head } from "next/document";
export class Card extends Head {
  render() {
    const data = Object.assign(source, target)
    return (
      <div>
        <h1>Hello title</h1>
      </div>
    );
  }
}

References

Nextjs Supported Browsers and Features

deepsourcestatus / test-repository

No ignore rules found