Using callback-passing for asynchronous actions does not compose well and creates complex flows of passing callbacks around. The JavaScript community has produced several libraries to cope with this.

While JavaScript itself is single-threaded, many JavaScript functions have supported asynchronous processing through callbacks (the variations on the jQuery AJAX function are just the most obvious ...

The WebAssembly JavaScript Promise Integration API suspends a Wasm application when it issues a synchronous API call and resumes it when the asynchronous I/O operation is completed.