How to wait until a callback is finished to return from ES6 Proxy

Question

I can't use promises because it force the user to convert everything to async functions for sync methods. Is there any way to force the proxy to not to return until the callback complete?

function callbackCase() {
    function saySomething(callback) {
        callback("Stackoverflow");
    }

    console.error = new Proxy(console.error, {
        apply: (target, thisArg, args) => {
            saySomething((result) => {
                return result;
            })
        }
    })

    let test = console.error();

    console.log("From Callback Case", test);
}




function nonCallbackCase() {
    console.errors = new Proxy(console.error, {
        apply: (target, thisArg, args) => {
            return "Stackoverflow";
        }
    })

    let test = console.errors();

    console.log("From Non Callback Case", test);
}


callbackCase()
nonCallbackCase()

Answer 1

Is there any way to force the proxy to not to return until the callback complete?

No, there is not. You can't make an asynchronous operation into a synchronous operation in Javascript. Anything you try to do (like looping on a flag) will just block the event loop and thus block your asynchronous operation from completing, so you'll be deadlocked.

There are three basic ways to communicate back the results or completion of an asynchronous operation, a callback, a promise or an event. You will need to use one of those mechanisms.

Said another way, you can't squeeze an asynchronous operation into a synchronous API. You have to change the API to be an asynchronous API. Returning a promise that is tied to your asynchronous operation is the modern way to do this in Javascript. This lets the caller, then use either .then() or await to monitor completion and the result of the operation.