I find MDN to be a bit clearer, and they benefit from the in-browser runtime. All the extra detail in the Rust docs (blanket traits etc) were quite intimidating and distracting when I first started learning it.
While both of these docs are pretty good, as someone who normally much prefers API references to "how to" formats, the MDN's "how to" approach here is succinct & just enough to cover reasonable bases, while the Rust API ref list is a bit too terse by comparison (& the Read More click out is a bit annoying).
https://doc.rust-lang.org/std/index.html