Async function without await in JavaScript

Mozilla documentation:

An async function can contain an await expression, that pauses the
execution of the async function and waits for the passed Promise's
resolution, and then resumes the async function's execution and
returns the resolved value.

As you assumed, if no await is present, the execution is not paused and your code will then be executed synchronously as normal.

Is possible to call async function without await keyword? and what happens if we call without await?

We use await when we need to call and wait for async function or Promise
In your case when you call it without await inside your componentDidMount, your function will work but your componentDidMount will not wait for that function to completely finishes.

Also if you don't want to use await and you don't want to wait inside componentDidMount, but you want to get notified when your async function finishes, you can use .then instead. Because async functions returns Promise

Here is your componentDidMount with .then
Notice that in this example this.doSomethingElse will call before the this.usrs is complete, and you only will be notified inside .then about your this.usrs result when it finished:

componentDidMount(){
    this.usrs(usrs).then(() => {
        // Your functions completely finished
    })
    .catch(err => {
        // There was an error
    });

    this.doSomethingElse();
}

How to safely call an async method in C# without await

If you want to get the exception "asynchronously", you could do:

  MyAsyncMethod().
    ContinueWith(t => Console.WriteLine(t.Exception),
        TaskContinuationOptions.OnlyOnFaulted);

This will allow you to deal with an exception on a thread other than the "main" thread. This means you don't have to "wait" for the call to MyAsyncMethod() from the thread that calls MyAsyncMethod; but, still allows you to do something with an exception--but only if an exception occurs.

Update:

technically, you could do something similar with await:

try
{
    await MyAsyncMethod().ConfigureAwait(false);
}
catch (Exception ex)
{
    Trace.WriteLine(ex);
}

...which would be useful if you needed to specifically use try/catch (or using) but I find the ContinueWith to be a little more explicit because you have to know what ConfigureAwait(false) means.

How to call async function asynchronously without awaiting for the result

This behavior will change depending upon the context.

• If you invoke this from a non-isolated context, then first and second will run on separate threads. In this scenario, the second task is not actually waiting for the first task, but rather there is a race as to which will finish first. This can be illustrated if you do something time-consuming in the first task and you will see the second task is not waiting at all.

  This introduces a race between first and second and you have no assurances as which order they will run. (In my tests, it runs second before first most of the time, but it can still occasionally run first before second.)

• However, if you invoke this from an actor-isolated context, then first will wait for second to yield before running.

So, the question is, do you really care which order these two tasks start? If so, you can eliminate the race by (obviously) putting the Task { await first() } after the call to second. Or do you simply want to ensure that second won’t wait for first to finish? In that case, this already is the behavior and no change to your code is required.

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You asked:

What if await first() needs to be run on the same queue as second() but asynchronously. … I am just thinking [that if it runs on background thread that it] would mean crashes due to updates of UI not from the main thread.

You can mark the routine to update the UI with @MainActor, which will cause it to run on the main thread. But note, do not use this qualifier with the time-consuming task, itself (because you do not want to block the main thread), but rather decouple the time-consuming operation from the UI update, and just mark the latter as @MainActor.

E.g., here is an example that manually calculates π asynchronously, and updates the UI when it is done:

func startCalculation() {
    Task {
        let pi = await calculatePi()
        updateWithResults(pi)
    }
    updateThatCalculationIsUnderway() // this really should go before the Task to eliminate any races, but just to illustrate that this second routine really does not wait
}

// deliberately inefficient calculation of pi

func calculatePi() async -> Double {
    await Task.detached {
        var value: Double = 0
        var denominator: Double = 1
        var sign: Double = 1
        var increment: Double = 0

        repeat {
            increment = 4 / denominator
            value += sign * 4 / denominator
            denominator += 2
            sign *= -1
        } while increment > 0.000000001

        return value
    }.value
}

func updateThatCalculationIsUnderway() {
    statusLabel.text = "Calculating π"
}

@MainActor
func updateWithResults(_ value: Double) {
    statusLabel.text = "Done"
    resultLabel.text = formatter.string(for: value)
}

Note: To ensure this slow synchronous calculation of calculatePi is not run on the current actor (presumably the main actor), we want an “unstructured task”. Specifically, we want a “detached task”, i.e., one that is not run on the current actor. As the Unstructured Concurrency section of The Swift Programming Language: Concurrency: Tasks and Task Groups says:

To create an unstructured task that runs on the current actor, call the Task.init(priority:operation:) initializer. To create an unstructured task that’s not part of the current actor, known more specifically as a detached task, call the Task.detached(priority:operation:) class method.

How can I call an async function without await?

One way would be to use create_task function:

import asyncio

async def handler_message(request):
    ...
    loop = asyncio.get_event_loop()
    loop.create_task(perform_message(x,y,z))
    ...

As per the loop documentation, starting Python 3.10, asyncio.get_event_loop() is deprecated. If you're trying to get a loop instance from a coroutine/callback, you should use asyncio.get_running_loop() instead. This method will not work if called from the main thread, in which case a new loop must be instantiated:

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)
loop.create_task(perform_message(x, y, z))
loop.run_forever()

Furthermore, if the call is only made once throughout your program's runtime and no other loop needs to be is instantiated (unlikely), you may use:

asyncio.run(perform_message(x, y, z))

This function creates an event loop and terminates it once the coroutine ends, therefore should only be used in the aforementioned scenario.

How can I call an async function without await?

One way would be to use create_task function:

import asyncio

async def handler_message(request):
    ...
    loop = asyncio.get_event_loop()
    loop.create_task(perform_message(x,y,z))
    ...

As per the loop documentation, starting Python 3.10, asyncio.get_event_loop() is deprecated. If you're trying to get a loop instance from a coroutine/callback, you should use asyncio.get_running_loop() instead. This method will not work if called from the main thread, in which case a new loop must be instantiated:

loop = asyncio.new_event_loop()
asyncio.set_event_loop(loop)
loop.create_task(perform_message(x, y, z))
loop.run_forever()

Furthermore, if the call is only made once throughout your program's runtime and no other loop needs to be is instantiated (unlikely), you may use:

asyncio.run(perform_message(x, y, z))

This function creates an event loop and terminates it once the coroutine ends, therefore should only be used in the aforementioned scenario.

Down-side on calling async function without await

Just remove the async from wierdFunction(). If you're not using the returned promise and not using await inside, then there's no reason to have it. It just creates an extra promise object for the return that then gets garbage collected so it creates extra overhead and it implies to the caller that the caller can use that promise for something useful.

Is there any advise against calling it without await keyword?

If your operation is truly "fire and forget" and you don't care about completion or reported errors, then it does not need to return a promise and you can just make it a normal function that initiates an asynchronous operation, but doesn't report any results.

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