javascript - $.each jquery 循环在 getJSON 请求后为每个元素打印一个 "undefined"，网格数据完美打印

Question

我正在执行一个 JSON 请求，在循环遍历元素之后，它们的行被完美打印。问题是，我不断看到我正在构建的网格顶部的每个元素都有一个未定义的打印，我该如何摆脱它？......

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;

}

Web 服务返回此 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

我认为你必须改变

function mostrarElementosViewMode(elem){

    var elemento;

到

function mostrarElementosViewMode(elem){

    var elemento = '';