You're confusing language and runtime environment. SVG lets you use ecmascript of some version in its <script> tags, it obviously doesn't provide browser api available to you from javascript in a browser.

> And that wasn't my point. SVG supports animation primitives. No need to animate through JS.

This isn't (AFAICT) animated via JS. (It's animated by a CSS animation, inside the SVG. TFA is wrong about the <animate> tag being what is leveraged.)