I was assuming that JavaScript would already be known to a certain degree.

I would actually recommend React over Angular for a beginner, because (assuming Angular 2 here) they're going to have to learn Typescript too. That's a big undertaking.

A beginner could also use plain old ES5 with a JSX transpiler right in web page with React.

VueJs might be a better choice than both of those, but much more limited job opportunities.