Macro embed_js::embed_js_preamble

macro_rules! embed_js_preamble {
    () => { ... };
}

For every crate that uses the js macro directly, the embed_js_preamble macro must be called at least once somewhere in the crate, for example

#[macro_use]
extern crate embed_js;

embed_js_preamble!();

#[no_mangle]
pub fn entry_point() {
    js!({console.log("Hello world!");});
}

You do not need to import embed_js at all in crates that only depend on crates that use the js macro without directly calling it themselves.