Angular 5 AudioContext issue on Safari

I'm trying to use AudioContext in my typescript file for an Angular 5 app. It works great on Chrome, doesn't work on Safari. Everything I see by googling says to use window.webkitAudioContext but that immediately blows up when the typescript compiler runs saying that it doesn't exist on type Window.

let context = new AudioContext();
let source = context.createBufferSource();
    .then(x => {
        source.buffer = x;