Cargo Features

fastrand = { version = "2.1.0", default-features = false, features = ["std", "alloc", "js"] }
default = std

The std feature is set by default whenever fastrand is added without default-features = false somewhere in the dependency tree.

std default js? = alloc
alloc std
js = getrandom, std

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

getrandom wasm32 wasm64 unknown js?