1. require the npm package the you need

const Buffer = require('buffer').Buffer

2. Append the variable to the window object

global.window.Buffer = Buffer

3. Install browserify as devDep

yarn add browserify -D

4. Compile your main.js file using browserify

browserify main.js -o output.js

5. use your output.js on your html

<script src="output.js" ></script>

6. run it on live server and check the window object on console if your npm package is present (in this example, it is Buffer)