angular-cli/docs/documentation/stories/global-lib.md

Global Library Installation

Some javascript libraries need to be added to the global scope and loaded as if they were in a script tag. We can do this using the scripts and styles options of the build target in angular.json.

As an example, to use Bootstrap 4 this is what you need to do:

First install Bootstrap from npm:

npm install jquery --save
npm install popper.js --save
npm install bootstrap --save

Then add the needed script files to scripts:

"scripts": [
  "node_modules/jquery/dist/jquery.slim.js",
  "node_modules/popper.js/dist/umd/popper.js",
  "node_modules/bootstrap/dist/js/bootstrap.js"
],

Finally add the Bootstrap CSS to the styles array:

"styles": [
  "node_modules/bootstrap/dist/css/bootstrap.css",
  "src/styles.css"
],

Restart ng serve if you're running it, and Bootstrap 4 should be working on your app.