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 apps[0].scripts and apps[0].styles properties of .angular-cli.json.

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

First install Bootstrap from npm:

npm install bootstrap@next

Then add the needed script files to apps[0].scripts:

"scripts": [
  "../node_modules/jquery/dist/jquery.js",
  "../node_modules/tether/dist/js/tether.js",
  "../node_modules/bootstrap/dist/js/bootstrap.js"
],

Finally add the Bootstrap CSS to the apps[0].styles array:

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

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