How to make Meteor methods synchronous?

Question

I need a way for a meteor call to be synchronous so that when a call is run, the code waits for a result to be done so it can continue to the next line of code on the client.

for example:

clientFunction = function(){

    Meteor.call('serverFunction', function(err,result){})//<--so when this gets a result and    
                                                    //is stored in a session variable
    var doSomeThing = Session.get('whatever') <-- so that your able to use it here
}

I've tried using a while loop to prevent anything from happening until a value is returned, but it seems like it runs after the clientFunction thus throwing it to its demise

any help would be appreciated

Answer 1

This is a very common question, being asked in various shapes and forms. Most people don't realize when they are making asynchronous calls. The solution, however, is always the same: wrap your method code on the server into a fiber or use a future.

The best practice, I think, is to use the currently available Meteor._wrapAsync function as described, e.g., here: Meteor: Calling an asynchronous function inside a Meteor.method and returning the result

Some other options are described here: https://gist.github.com/possibilities/3443021

---

Update: The method is now called Meteor.wrapAsync.

Answer 2

Put the code that you want to run after the method completes into the method callback. This is standard for any asynchronous javascript.

clientFunction = function(){
  Meteor.call('serverFunction', function(err, result){
    if (err) {
      alert(err);
    } else {
      Session.set('whatever', result.whatever);
    }
  });
};

That sets the value of the session variable once the method call returns. Now you use Meteor's reactivity to use that variable:

Template.hello.helpers({
  myWhatever: function () {
    var whatever = Session.get('whatever');

    if (whatever) return whatever;

    return 'Loading whatever...';
  }
});

Answer 3

I followed this tutorial and do something like below

This is a meteor server side method

productIdResult:function(searchstring)
{
   {
      var skimlinks_query = Async.wrap(skimlinks.query);
      var title_val="title:\"electric bicycle\"  AND merchantCategory:*bikes*";                     
      var result = skimlinks_query({
                        searchFor: searchstring,
                        start:start,
                        rows:rows,
                        fq: "country:US"
                    });
      return result;
}

And I call it from client like this

Meteor.call('productIdResult',
            searchstring,
            function(error,resul)
            {
                arr[0]=resul.skimlinksProductAPI.products[0].title;
                $( "#op1").autocomplete({source:arr});

            }
);

Note that it is not synchronous, but you get the return value in the callback