Calling closures via WebAssembly

The official Rust book defines closures as follows:

Closures are anonymous functions which you can save in a variable or can be passed as arguments to other functions. - The Rust Programming Language (Covers Rust 2018) by Steve Klabnik and Carol Nichols (https://doc.rust-lang.org/book/ch13-00-functional-features.html)

MDN defines a closure for JavaScript as follows:

A closure is the combination of a function and lexical environment within which that function was declared.- MDN Web Docs (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures#closure)

In general, closures are self-contained blocks of functionality that are tossed around and used in the code. They can capture and store references to the variables from the context in which they are defined.

Closures and functions are similar except for a subtle difference. Closures will capture the state when it is first created. Then, whenever a closure is called, it closes over...