Don't worry about the fact that we're redeclaring the foo function for every component instance — Svelte will hoist any functions that don't depend on local state out of the component definition.

can be used to avoid variable hoisting from within blocks

For that reason, it is recommended to always declare variables at the top of their scope (the top of global code and the top of function code) so it's clear which variables are function scoped (local) and which are resolved on the scope chain.