asyncJsFromJava.java

// Expose a JS asynchronous function to Java
Value asyncFunction = context.eval("js", "(async function(x) { return x; })");
// Invoke the function. The result is a JavaScript Promise object
Value jsPromise = asyncFunction.execute(42);
// Register promise reactions
jsPromise.invokeMember("then", (Consumer<Object>) (result) -> {
  System.out.println("JavaScript resolves: " + result);
})
.invokeMember("catch", (Consumer<Throwable>) (error) -> {
  System.out.println("JavaScript rejects: " + error);
});