Bind API returned data to dropdownlist

I am trying to bind a dropdown list via javascript/jquery (anyone will work). Here is my code I tried -

$(document).ready(function () {  
   $.ajax({  
       type:"POST",
     url: "function.php",
     //dataType: "json"
     success: function(result){
     alert(result);
        for (var i in result) {
            $("#dropdownlist").append('<option value="'+result[i]+'">'+result[i]+'</option>');
    };

     }
  });

});

On alert, it is showing data like this -

{"BU_CODE_RU":"DK"}{"BU_CODE_RU":"PL"}{"BU_CODE_RU":"SA"}{"BU_CODE_RU":"SP"}{"BU_CODE_RU":"RS"}{"BU_CODE_RU":"IS"}{"BU_CODE_RU":"SE"}{"BU_CODE_RU":"LT"}{"BU_CODE_RU":"GR"}{"BU_CODE_RU":"AT"}{"BU_CODE_RU":"DE"}{"BU_CODE_RU":"TR"}{"BU_CODE_RU":"CZ"}{"BU_CODE_RU":"US"}{"BU_CODE_RU":"TW"}{"BU_CODE_RU":"TH"}{"BU_CODE_RU":"EG"}{"BU_CODE_RU":"SI"}{"BU_CODE_RU":"HU"}{"BU_CODE_RU":"JP"}{"BU_CODE_RU":"IN"}{"BU_CODE_RU":"CA"}{"BU_CODE_RU":"UNK"}{"BU_CODE_RU":"MA"}{"BU_CODE_RU":"NL"}{"BU_CODE_RU":"RU"}{"BU_CODE_RU":"HK"}{"BU_CODE_RU":"ID"}{"BU_CODE_RU":"FR"}{"BU_CODE_RU":"IT"}{"BU_CODE_RU":"ES"}{"BU_CODE_RU":"NO"}{"BU_CODE_RU":"BE"}{"BU_CODE_RU":"KR"}{"BU_CODE_RU":"MY"}{"BU_CODE_RU":"FI"}{"BU_CODE_RU":"DO"}{"BU_CODE_RU":"KW"}{"BU_CODE_RU":"SK"}{"BU_CODE_RU":"GB"}{"BU_CODE_RU":"AE"}{"BU_CODE_RU":"IL"}{"BU_CODE_RU":"BG"}{"BU_CODE_RU":"AUW"}{"BU_CODE_RU":"SG"}{"BU_CODE_RU":"BH"}{"BU_CODE_RU":"QA"}{"BU_CODE_RU":"LV"}{"BU_CODE_RU":"AU"}{"BU_CODE_RU":"HR"}{"BU_CODE_RU":"CY"}{"BU_CODE_RU":"IE"}{"BU_CODE_RU":"UA"}{"BU_CODE_RU":"CE"}{"BU_CODE_RU":"CN"}{"BU_CODE_RU":"CH"}{"BU_CODE_RU":"RO"}{"BU_CODE_RU":"PT"}{"BU_CODE_RU":"PH"}{"BU_CODE_RU":"JO"}

How to bind those values to Dropdown List (Only Value). It will be better if I can add Default Value something like "Select Country".

If response is a string, you can use a regex

const data = `{"BU_CODE_RU":"DK"}{"BU_CODE_RU":"PL"}{"BU_CODE_RU":"SA"}{"BU_CODE_RU":"SP"}{"BU_CODE_RU":"RS"}{"BU_CODE_RU":"IS"}{"BU_CODE_RU":"SE"}{"BU_CODE_RU":"LT"}{"BU_CODE_RU":"GR"}{"BU_CODE_RU":"AT"}{"BU_CODE_RU":"DE"}{"BU_CODE_RU":"TR"}{"BU_CODE_RU":"CZ"}{"BU_CODE_RU":"US"}{"BU_CODE_RU":"TW"}{"BU_CODE_RU":"TH"}{"BU_CODE_RU":"EG"}{"BU_CODE_RU":"SI"}{"BU_CODE_RU":"HU"}{"BU_CODE_RU":"JP"}{"BU_CODE_RU":"IN"}{"BU_CODE_RU":"CA"}{"BU_CODE_RU":"UNK"}{"BU_CODE_RU":"MA"}{"BU_CODE_RU":"NL"}{"BU_CODE_RU":"RU"}{"BU_CODE_RU":"HK"}{"BU_CODE_RU":"ID"}{"BU_CODE_RU":"FR"}{"BU_CODE_RU":"IT"}{"BU_CODE_RU":"ES"}{"BU_CODE_RU":"NO"}{"BU_CODE_RU":"BE"}{"BU_CODE_RU":"KR"}{"BU_CODE_RU":"MY"}{"BU_CODE_RU":"FI"}{"BU_CODE_RU":"DO"}{"BU_CODE_RU":"KW"}{"BU_CODE_RU":"SK"}{"BU_CODE_RU":"GB"}{"BU_CODE_RU":"AE"}{"BU_CODE_RU":"IL"}{"BU_CODE_RU":"BG"}{"BU_CODE_RU":"AUW"}{"BU_CODE_RU":"SG"}{"BU_CODE_RU":"BH"}{"BU_CODE_RU":"QA"}{"BU_CODE_RU":"LV"}{"BU_CODE_RU":"AU"}{"BU_CODE_RU":"HR"}{"BU_CODE_RU":"CY"}{"BU_CODE_RU":"IE"}{"BU_CODE_RU":"UA"}{"BU_CODE_RU":"CE"}{"BU_CODE_RU":"CN"}{"BU_CODE_RU":"CH"}{"BU_CODE_RU":"RO"}{"BU_CODE_RU":"PT"}{"BU_CODE_RU":"PH"}{"BU_CODE_RU":"JO"}`

// success: function(data) {
 
   var options = data.match(/:"(\w+)/g)
  .map(cc => { 
    cc = cc.replace(/\W+/g,""); // remove non-letters
    return `<option value="${cc}">${cc}</option>`;
  });
 
   $("#dropdownlist").append(options);
 
// }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<select id="dropdownlist">
<option value="">Please select</option>
</select>

Even more elegant using lookbehind, pointed out to me by Jonathan Lam

const data = `{"BU_CODE_RU":"DK"}{"BU_CODE_RU":"PL"}{"BU_CODE_RU":"SA"}{"BU_CODE_RU":"SP"}{"BU_CODE_RU":"RS"}{"BU_CODE_RU":"IS"}{"BU_CODE_RU":"SE"}{"BU_CODE_RU":"LT"}{"BU_CODE_RU":"GR"}{"BU_CODE_RU":"AT"}{"BU_CODE_RU":"DE"}{"BU_CODE_RU":"TR"}{"BU_CODE_RU":"CZ"}{"BU_CODE_RU":"US"}{"BU_CODE_RU":"TW"}{"BU_CODE_RU":"TH"}{"BU_CODE_RU":"EG"}{"BU_CODE_RU":"SI"}{"BU_CODE_RU":"HU"}{"BU_CODE_RU":"JP"}{"BU_CODE_RU":"IN"}{"BU_CODE_RU":"CA"}{"BU_CODE_RU":"UNK"}{"BU_CODE_RU":"MA"}{"BU_CODE_RU":"NL"}{"BU_CODE_RU":"RU"}{"BU_CODE_RU":"HK"}{"BU_CODE_RU":"ID"}{"BU_CODE_RU":"FR"}{"BU_CODE_RU":"IT"}{"BU_CODE_RU":"ES"}{"BU_CODE_RU":"NO"}{"BU_CODE_RU":"BE"}{"BU_CODE_RU":"KR"}{"BU_CODE_RU":"MY"}{"BU_CODE_RU":"FI"}{"BU_CODE_RU":"DO"}{"BU_CODE_RU":"KW"}{"BU_CODE_RU":"SK"}{"BU_CODE_RU":"GB"}{"BU_CODE_RU":"AE"}{"BU_CODE_RU":"IL"}{"BU_CODE_RU":"BG"}{"BU_CODE_RU":"AUW"}{"BU_CODE_RU":"SG"}{"BU_CODE_RU":"BH"}{"BU_CODE_RU":"QA"}{"BU_CODE_RU":"LV"}{"BU_CODE_RU":"AU"}{"BU_CODE_RU":"HR"}{"BU_CODE_RU":"CY"}{"BU_CODE_RU":"IE"}{"BU_CODE_RU":"UA"}{"BU_CODE_RU":"CE"}{"BU_CODE_RU":"CN"}{"BU_CODE_RU":"CH"}{"BU_CODE_RU":"RO"}{"BU_CODE_RU":"PT"}{"BU_CODE_RU":"PH"}{"BU_CODE_RU":"JO"}`

// success: function(data) {
  $("#dropdownlist").append(
    data.match(/(?<=:")(\w+)/g)
    .map(cc => `<option value="${cc}">${cc}</option>`)
  )

// }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<select id="dropdownlist">
  <option value="">Please select</option>
</select>

_{Note: Browser support for JS RegExp lookbehind (ES2018 draft) is still low. See the compatibility table on MDN for more details.}

Original answer for simpler format ({"DK"}{"PL"}{"SA"}....) :

var options = data.match(/[A-Z]{2,}/g).map(cc => `<option value="${cc}">${cc}</option>`)

const data = `{"DK"}{"PL"}{"SA"}{"SP"}{"RS"}{"IS"}{"SE"}{"LT"}{"GR"}{"AT"}{"DE"}{"TR"}{"CZ"}{"US"}{"TW"}{"TH"}{"EG"}{"SI"}{"HU"}{"JP"}{"IN"}{"CA"}{"UNK"}{"MA"}{"NL"}{"RU"}{"HK"}{"ID"}{"FR"}{"IT"}{"ES"}{"NO"}{"BE"}{"KR"}{"MY"}{"FI"}{"DO"}{"KW"}{"SK"}{"GB"}{"AE"}{"IL"}{"BG"}{"AUW"}{"SG"}{"BH"}{"QA"}{"LV"}{"AU"}{"HR"}{"CY"}{"IE"}{"UA"}{"CE"}{"CN"}{"CH"}{"RO"}{"PT"}{"PH"}{"JO"}`

// success: function(data) {
var options = data.match(/[A-Z]{2,}/g).map(cc => `<option value="${cc}">${cc}</option>`)
$("#dropdownlist").append(options);
// }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<select id="dropdownlist">
  <option value="">Please select</option>
</select>