In the modern browsers you can use the fetch to download resource (Mozilla docs) and then eval to execute it.
For example to download Angular1 you need to type:
fetch('https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js')
.then(response => response.text())
.then(text => eval(text))
.then(() => { /* now you can use your library */ })