easyui return undefined from ajax

I make form submit, when I check in console it returns JSON data. But I can't use object in JSON data.

$('#ff').form({
                type: 'POST',
                cache: false,
                url: base_url + 'Api/lapor/submit',
                dataType: 'json',
                iframe: false,
                onSubmit: function(param) {
                    param.id_item = sessionStorage.id_item;
                    param.token = sessionStorage.token;
                },
                onProgress: function(percent) {
                    $.messager.progress();
                },
                success: function(msg){
                  console.log(msg.status); //it will return undefined
                  $.messager.progress('close');
                },
                onLoadError: function(){
                    $.messager.alert('Error', 'Gagal', 'error');
                }
            });

I try console.log(msg) and it return JSON data console

When you log the return message using console.log(msg.status);, if it write the result as {message: "Data 1 telah disimpan", status: true} then you can call it by using either msg.status or msg['status']

But in your case it's logged as {"message": "Data 1 telah disimpan", "status": true}, so you should try calling it with the " included like msg['"status"'] or msg["\"status\""]

var msg1 = {"message": "Data 1 telah disimpan", "status": true}
var msg2 = {'"message"': "Data 2 telah disimpan", '"status"': true}

function checkdata1() {
  console.log(msg1);
  alert(msg1.message);
}

function checkdata2() {
  console.log(msg2);
  alert(msg2['"message"'])
}

<btn onclick="checkdata1()">Check Data 1</btn>
<br/>
<btn onclick="checkdata2()">Check Data 2</btn>

Update Here's the difference between the msg1 and msg2 when logged using console.log

Update 2 Because the return type of jeasyui $.form is a string, so you need to parse it first to a JSON / javascript object by using JSON.parse or the one found in the jeasyui docs section Handle submit response here