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I have this:

var myError; function getNames(user,location){ myError=null; //Make an Ajax Call (this takes some time) //On Success do this: if(//Some Condition){ myError=false; }else{ myError=true } } function first(){ getNames(user, location); if(myError==false){ //MYCONDITION //do some custom stuff just for first(); }else{ alert("Failed"); } } function second(){ getNames(user, location); if(myError==false){ //MYCONDITION //do some custom stuff just for second(); }else{ alert("Failed"); } }

Now, when I call first() or second() it always gives me alert message "FAILED". The problem is that //MYCONDITION is being executed before the getNames() function finishes. I want to wait for getNames() to execute before I can check //MYCONDITION.

I cannot set a delay since I don't know how much time getNames() is going to take. I was thinking about using some jQquery function but I cannot seem to find one.

And, I am trying to keep the getNames() as generic as possible. So, I am thinking of a way to not disturb the getNames().

The last option I see is adding callback() to getNames(). But, this function is being called by other functions too that won't need callback().

Any thoughts guys?

Thanks.

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  • what does the ajax call look like? are you using jquerys $.ajax()? Commented Sep 13, 2012 at 16:23
  • The getNames() function did finish (return). It's just that Ajax requests are asynchronous. Commented Sep 13, 2012 at 16:24

2 Answers 2

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It's totally fine adding a callback; you can just check if it exists:

function getNames(user, location, callback){ myError=null; //Make an Ajax Call (this takes some time) //On Success do this: if(//Some Condition){ myError=false; }else{ myError=true } if(callback) { callback.apply(); } }

If you're bothered by the arity not being generic enough, you can have the function accept an object instead of arguments, so:

function getNames(options) { var user = options.user; var location = options.loacation; var callback = options.callback; myError=null; //Make an Ajax Call (this takes some time) //On Success do this: if(//Some Condition){ myError=false; }else{ myError=true } if(typeof callback !== "undefined") { callback.apply(); } }

And when you call getNames, you can do:

getNames({ user: "some user", location: "some location", callback: function() { ... } });

or

getNames({ user: "some user", location: "some location" });
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1 Comment

Thanks for the great explanation and code example. But, at this time I think I would just go with async: false option. Still thanks a lot for taking time and effort. :)
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In jquery, if you don't like callbacks (which I highly hope you don't :) ) , you're in luck my friend. There is a flag in the $.ajax() function that you can use to turn async off for that specific AJAX request. Below is code sample:

http://api.jquery.com/jQuery.ajax/

var x = 1; jQuery.ajax({ url: 'http://example.com/catalog/create/', success: function(result) { x = 59; }, async: false }); console.log(x); //Should print 59 instead of 1
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4 Comments

async is not recommended. It's not good practice from a UI perspective to block the main UI thread.
Hrmmm from his code, I don't think he is not doing much UI. He is just populating some field with names I believe. I do agree with you that callbacks are awesome. I am just providing an alternative approach and clarifying what async is and how to get around it using standard API from jquery (notice how async is not deprecated, yet...).
Sometimes bigger problems have simpler solutions. why didn't I think of this before. Thanks Phu!
Hey no problem. Just trying to help. At first, I ran into the same problem like you to and was pounding my head! I was like... this code is not working correctly and that it is NOT executing top down! From where I came from (java and ruby), this was never a problem until javascript came along. Glad to help buddy, good luck :)

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