how to make Javascript setTimeout returns value in a function

Question

I have a function that calls some service and returns the response. If the response is FALSE, it waits 1 second to ask the service again (which then probably returns TRUE).

How can I do to call my function "checkService()" once, and get the real value? (the first or second try, decided by the function) I set the RET value inside the function, but the functions always return the first RET, because the setTimeout is asynchronous.

In other words, I need some "sleep" trick, or any solution (may be jQuery too).

function checkService() {

  //this may return TRUE or FALSE
  var RET = someServiceResponse(); 

  // here waits 1 second, then ask the service again
  if( RET == true ) {
    return true;
  } else {

    setTimeout(
        function() {
            //it must return the second response of the service
            RET = someServiceResponse();  
        }, 
        1000
    );

    // I want the checkService() return the response after de timeout
    return RET;  
  }
}

function alertResponse() {
    alert( checkService() );
}

Is someServiceResponse getting its result from an ajax call? That may be the heart of your issue. — Travis J
– Travis J, Commented Aug 4, 2014 at 23:28
although the 1 sec wait seems useful, its easily broken if the call takes more time to return. I would recommend splitting up this functionality with a callback function that fires when the response is actually delivered. — Bosworth99
– Bosworth99, Commented Aug 4, 2014 at 23:31
Travis, no. However, I dont mind if waits takes more than 1 second. It's not important that time, just need to wait some (half second or so) and chek it again — Aberel
– Aberel, Commented Aug 5, 2014 at 0:04

Raphaël Malié · Accepted Answer · 2014-08-05 00:32:20Z

3

You should use a callback function when you expect a result from the service.

Like this :

function checkService(callback) {

    //this may return TRUE or FALSE
    var RET = someServiceResponse();

    // here waits 1 second, then ask the service again
    if( RET == true ) {
        callback(RET);
    } else {

        setTimeout(
                function() {
                    //it must return the second response of the service
                    RET = someServiceResponse();
                    callback(RET);
                },
                1000
        );

        // I want the checkService() return the response after de timeout
        return RET;
    }
}

So when you want to call the service, you just need to do :

checkService(function(status){
    alert(status);

    // Here some code after the webservice response
});

edited Aug 5, 2014 at 0:32

answered Aug 4, 2014 at 23:31

Raphaël Malié

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2 Comments

Rebirth Over a year ago

or call checkService() again in the timeout function. should work either way.

Aberel Over a year ago

I've used alert() to simplify the thing. Actually I need to call checkService() from many other funcions in my code, and do whatever needed according to the response of checkService(). If I call it again from outside, I would doing the same that checkService() does. That's because I made the function checkService().

elzi · Accepted Answer · 2014-08-04 23:33:02Z

0

Googling 'javascript setTimeout callback' here's a handy jsFiddle about 3 results down:

getData('http://fakedomain1234.com/userlist', writeData);

document.getElementById('output').innerHTML += "show this before data ...";

function getData(dataURI, callback) {
    // Normally you would actually connect to a server here.
    // We're just going to simulate a 3-second delay.
    var timer = setTimeout(function () {
        var dataArray = [123, 456, 789, 012, 345, 678];
        callback(dataArray);
    }, 3000);
}

function writeData(myData) {
    console.log(myData);
}

http://jsfiddle.net/cwbuecheler/Y9Ca8/

answered Aug 4, 2014 at 23:33

elzi

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