$ .each jquery循环在getJSON请求之后为每个元素打印一个“未定义”，网格数据可以完美打印

Question

I'm doing a JSON request and after I loop through the elements and they rows are printed perfectly. The thing is that I keep seeing one undefined printing for every element on the top of the grid I'm building, How do I get rid of it?......

undefinedundefinedundefinedundefinedundefinedundefinedundefinedundefinedundefinedundefinedundefined

 $("#newsletters").click(function(){
        $.getJSON("/newsletter/getNewsletters", function(result){

            var grid="<br><table id='newsletter_grid'>";
            grid+="<thead><tr><th></th><th>Año</th><th>Mes</th><th>Quincena</th><th></th><th></th><th>Publicado</th></tr></thead>";

             grid+="<tr><td><button id='agregar_button' onclick='crearNuevoNewsLetter()'>Nuevo</button></td></tr>";

             $.each(result, function(i, elem){

                    //show view fieldset, son los campos que se muestran para visualizar los datos

                    grid+=mostrarElementosViewMode(elem);               

                    //crea los hidden fields asociados a los view fields creados arriba de este

                    grid+=crearRowHidden(elem);


                });


            grid+="</table>";

            $("#grilla").html(grid);


        });




    }); 

function mostrarElementosViewMode(elem){

    var elemento;

    elemento+="<tr id='fieldset_"+elem.id+"'>";

    elemento+="<td><input type='hidden' value='"+elem.id+"'></td>";

    elemento+="<td id='anio_view_"+elem.id+"'>"+elem.anio+"</td>";

    elemento+="<td id='mes_view_"+elem.id+"'>"+elem.mes+"</td>";

    elemento+="<td id='quincena_view_"+elem.id+"'>"+elem.quincena+"</td>";

    elemento+="<td><button id='editar_"+elem.id+"' value='Editar' onclick='muestraEditarFieldsNewsletter(\""+elem.id+"\")'>Editar</td>";

    elemento+="<td><button id='eliminar_newsletter_"+elem.id+"' value='Eliminar'>Eliminar</td>";

    if(elem.publicado == 1){
        elemento+="<td><input type='checkbox' id='publicado_view_"+elem.id+"' name='publicado' checked='checked'></td>";
    } else {
        elemento+="<td><input type='checkbox' id='publicado_view_"+elem.id+"' name='publicado'></td>";
    }

     elemento+="</tr>";

    return elemento;

}   

function crearRowHidden(elem){

    var nuevoHiddenFieldSet="";

    nuevoHiddenFieldSet+="<tr id='fieldset_hidden_"+elem.id+"' style='display:none'>";

    nuevoHiddenFieldSet+="<td><input type='hidden' value='"+elem.id+"'></td>";

    nuevoHiddenFieldSet+="<td><input name='anio' value='"+elem.anio+"' id='anio_"+elem.id+"' /></td>";

    nuevoHiddenFieldSet+="<td><input name='mes' value='"+elem.mes+"' id='mes_"+elem.id+"' /></td>";

    nuevoHiddenFieldSet+="<td><input name='quincena' value='"+elem.quincena+"' id='quincena_"+elem.id+"' /></td>";

    nuevoHiddenFieldSet+="<td><button value='Guardar' name='guardar_newsletter' id='guardar_newsletter_"+elem.id+"' onclick='guardarNewsletter("+elem.id+",\"update\")'>Guardar</td>";

    nuevoHiddenFieldSet+="<td></td>";

    if(elem.publicado==1){
        nuevoHiddenFieldSet+="<td><input type='checkbox' id='publicado_"+elem.id+"' name='publicado' checked='checked'></td>";
    }else{
        nuevoHiddenFieldSet+="<td><input type='checkbox' id='publicado_"+elem.id+"' name='publicado'></td>";
    }

    nuevoHiddenFieldSet+="</tr>";

    return nuevoHiddenFieldSet;

}

and the web service returns this JSON:

[{"id":"12","anio":"2016","mes":"1","quincena":"4","publicado":"1"},{"id":"11","anio":"0000","mes":"1"
,"quincena":"1","publicado":"1"},{"id":"10","anio":"2000","mes":"1","quincena":"1","publicado":"1"},
{"id":"9","anio":"2000","mes":"1","quincena":"5","publicado":"1"},{"id":"8","anio":"0000","mes":"1","quincena"
:"1","publicado":"1"},{"id":"6","anio":"0000","mes":"1","quincena":"3","publicado":"1"},{"id":"5","anio"
:"2016","mes":"1","quincena":"5","publicado":"1"},{"id":"4","anio":"2016","mes":"1","quincena":"4","publicado"
:"1"},{"id":"3","anio":"2016","mes":"1","quincena":"3","publicado":"1"},{"id":"2","anio":"2016","mes"
:"1","quincena":"2","publicado":"1"},{"id":"1","anio":"2016","mes":"2","quincena":"1","publicado":"1"
}]

Answer 1

I think you must change

function mostrarElementosViewMode(elem){

    var elemento;

to

function mostrarElementosViewMode(elem){

    var elemento = '';