`#[js(callable)]`

Use #[js(callable)] to store JavaScript functions as values while declaring their signatures.

This could be used to describe functions that return other functions:

use ferrosaur::js;

#[js(value)]
struct Logger;

#[js(callable)]
impl Logger {
    fn call(&self, message: serde<&str>) {}
}

#[js(value)]
struct Logging;

#[js(interface)]
impl Logging {
    #[js(func)]
    fn with_prefix(&self, prefix: serde<&str>) -> Logger {}
}

// Expressed in TypeScript:

interface Logger {
  (message: string): void;
}

interface Logging {
  with_prefix: (prefix: string) => Logging;
  //           (prefix: string) => (message: string) => void
}

Use js(callable) on an impl block, which must contain a single item, a function named call, whose signature follows the same usage as js(func).

tip

JavaScript does not have a proper "callable interface." This is named callable to distinguish it from js(func), which is for describing named functions accessible from an object.