Why can not I get value returned by function?

Question

Why can not I get value returned by function?

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#1 by (4 votes)

2

I can not get the value returned from the function, what would be the reason? Could someone help me?

In my HTML page I have the following function:

function montarCursos(){
            var cursos = controller.getCursos();

            if(cursos != null){
                for(var i = 0; i < cursos.length; i++){
                    $("#cursos").append('<button class="ui-btn ui-corner-all" data-transition ="slide" onclick="controller.setNomeCurso("' + cursos[i].Value +'")">' + cursos[i].Name + '</button>')
                }
            }   
        }

Controller.js

var controller = {
getCursos: function () {

        function carregarCursos() {
            var resultado = [];
            var cursos = new cursosDao();
            resultado = cursos.getCursos();
            if (resultado.length > 0) {
                return resultado;
            } else {
                return null;
            }
        }
        loadDependence("Dao/cursosDao.js", carregarCursos);
    }
}

loadDependence.js :

function loadDependence(url, callback) {

    var head = document.getElementsByTagName('head')[0];
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.src = url;
    script.onreadystatechange = callback;
    script.onload = callback;
    head.appendChild(script);
}

cursosDao.js

function cursosDao() {
    this.getCursos = function() {
        var cursos = [];
        cursos.push({
            "Value" : "Anáse de Sistemas",
            "Name" : "Anáse de Sistemas"
        });

        cursos.push({
            "Value" : "Ciência da Computação",
            "Name" : "Ciência da Computação"
        });

        return cursos;
    }
}

javascript

asked by anonymous 04.06.2015 / 23:20

1 answer

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score 4 · Accepted Answer

The problem is that return within function carregarCursos only applies to carregarCursos . It will not "jump out" and serve to return a pro getCursos value. In the way your code is written, getCursos will always return undefined , without waiting for the courses to load.

One way to check this is to put a console.log at the end:

getCursos: function () {
    /*...*/
    loadDependence("Dao/cursosDao.js", carregarCursos);
    console.log("Nao está esperando pelo loadDependence...");
    return 17; // E está chegando no final da função 
}

Unfortunately, it does not have a pretty good idea to solve this problem in Javascript. You will have to make getCursos use an API with callbacks instead of returning the list of courses.

getCursos: function (onDone) {
    loadDependence("Dao/cursosDao.js", function() {
        var resultado = [];
        var cursos = new cursosDao();
        cursos.getCursos(function(resultado){
            if (resultado.length > 0) {
                onDone(resultado);
            } else {
                onDone(null);
            }
        });
    });
}

controller.getCursos(function(cursos){
  if(cursos != null){
    for(var i = 0; i < cursos.length; i++){
      /*...*/
    }
  }
}

In this example I also assumed that cursos.getCursos might have to make an asynchronous request and therefore would also need to return the value via callback. If you do not need to request, you can continue using the synchronous interface you were already using.