Luckily, you can use the amazing polyfill service polyfill.io, to polyfill the required features for you based on your browser user-agent.
<script src="https://cdn.polyfill.io/v2/polyfill.js?features=es6&flags=gated"></script> <script src="https://unpkg.com/spiritjs/dist/spirit.min.js"></script>
Always test your animations in other browsers to make sure it renders correctly. Checkout the Polyfill.io docs for more info about polyfilling browser features.
Pascal Klau has created a dynamic-polyfill package on npm, which only polyfill missing features to minimize browser requests.
The runtime uses GSAP for animation playback. GSAP does a great job on cross-browser support and performance, yet it might be possible that a certain property cannot be animated on older browsers.
Always test you animations in different browsers.