Question

I have a function matcher which is called every time a keyup event is sent.

This function belongs to a module which look like this (1).
what if another call is done before the fetching is completed?
How can I solve this problem in this module (1)?

---

(1)

(function ($, UserCollection) {

    var userCollection;

    var matcher = function (request, response) {
        if (!userCollection) {
            userCollection = new UserCollection();
            userCollection.fetch();
        } else {
            isMatched(request, response);
        }
    };

    return matcher;
}(jquery, UserCollection));

Answer 1

I’ll take a different, probably overkill, approach and use the jqXHR object returned by collection.fetch.

var Matcher=(function($,UserCollection) {

    var xhr=null, userCollection=null;

    // matching against a defined ID for testing purpose
    function isMatched(id) {
        return userCollection.get(id);
    }

    // the request would be an ID in my example,
    // and the callback is the function invoked when the collection is fetched
    function matcher(request, callback) {
        if (!xhr) {
            userCollection = new UserCollection();

            // fetch returns a handy xhr object used for the deferred
            xhr=userCollection.fetch(); 
        }

        xhr.then(function() {
            callback(isMatched(request));
        });
    }       

    return matcher;

})(jQuery, UserCollection);

If the xhr is already resolved, the callback is immediately invoked, if not, it will be when the request completes : see jQuery.Deferred for more info.

And you would use it as

Matcher(1,console.log);
Matcher(2,console.log);

And a Fiddle http://jsfiddle.net/EWSAV/1/