JS模块模式中的AJAX

Question

I'm creating an application using Module Pattern in JS. I've create two modules and I have this code:

var dataController = (function () {
    var request = new XMLHttpRequest();

    var getFilmes = function () {
        request.onreadystatechange = function() {
            if(request.readyState === 4) {
                if(request.status === 200) {
                    var obj = JSON.parse(request.responseText);
                    return obj; 
                } else {
                    console.log('An error occurred during your request: ' +  request.status + ' ' + request.statusText);
                } 
            }
        }

        request.open('Get', 'http://localhost:8080/api/filmes/5b8947446f506266bc522f38');
        request.send();
    }

    return {
        filmes: function (){
            return getFilmes();

        }
    };

})();

var controller = (function (dataCtrl) {

    var preencheFilmes = function(){
        var obj = dataCtrl.filmes();
        console.log(obj);

    }

    return {
        init: function(){
            console.log("APP START");
            preencheFilmes();
        }
    };

})(dataController, UIController);


controller.init();

The problem is that I can't get the response from AJAX when I'm calling preencheFIlmes in the "init". But I can get the result in the dataController.

Someone can help me? I'm learning how to work with this pattern.

Thank you so much.

Answer 1

Your function getFilmes() is asynchronous and doesn't return anything. A simple solution is to add a callback parameter like this:

var getFilmes = function(callback) {
    request.onreadystatechange = function() {
        if(request.readyState === 4) {
            if(request.status === 200) {
                var obj = JSON.parse(request.responseText);
                callback(obj); // <-- calls the callback function
            } else {
                ...
            } 
        }
    }
    ...
}

Then you can pass an anonymous callback function when you want to get the results:

var preencheFilmes = function(){
    dataCtrl.filmes(function(obj) {
        console.log(obj);
    });
}

Another option is to use the async/await feature, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function