How to retrieve a single element value from a json response using jQuery?

i want to display only item id's "ia_itemid" in a select drop down list using jquery

I cannot see the drop down DOM ,instead only ajax & it's response

If you want to get ia_itemid you can use forEach array method and create an array containing value of ia_itemid

    var a = {
   "completed":true,
   "totalItems":98891,
   "items": [
        {"ia_biserial":"",
    "ia_bloomstaxonomy":"Creating"
    ,"ia_correctanswer":"",
    "ia_difficulty":"High",
    "ia_dok":"IV",
    "ia_extid":"231617",
    "ia_gradelevel":"GradeK",
    "ia_hasimages":"False",
    "ia_itemid":1,
    "ia_lang":"English",
    "ia_pointvalue":"2",
    "ia_pvalue":"",
    "ia_subject":"Math",
    "ia_teitype":"OR","ia_vendorid":"i-321813",
    "passages":[],
    "standards":[]
     },

    {
  "ia_biserial":"",
    "ia_bloomstaxonomy":"Creating",
    "ia_correctanswer":"",
    "ia_difficulty":"High",
    "ia_dok":"IV",
    "ia_extid":"231616",
    "ia_gradelevel":"GradeK",
    "ia_hasimages":"False",
    "ia_itemid":2,
    "ia_lang":"English",
    "ia_pointvalue":"2",
    "ia_pvalue":"",
    "ia_subject":"Math",
    "ia_teitype":"OR",
    "ia_vendorid":"i-321812",
    "passages":[],
    "standards":[]
    },
    ]
}

var _getItem = a.items;
var _filter = []
_getItem.forEach(function(item){
           _filter.push(item.ia_itemid)
})
var _options =""; 
// loop through _filter and create options
_filter.forEach(function(item){
   _options +='<option value="demo_'+item+'">'+item+'</option>'
})
$("#demoApp").append(_options); //Append with select element

JSFIDDLE

Usually it's best to break your problem down into parts and then research each part. In your case, you need to:

• Retrieve data from a server that delivers it as JSON - see get json data with jquery (and many, many more of those)

• Get just one property from each of the objects in an array - see From an array of objects, extract value of a property as array et. al.

• Use that property to add options to a select box - see Adding options to a <select> using jQuery/JavaScript et. al.

Basically:

// Retrieve the data as JSON and parse it (automatically)
$.getJSON("https://api.certicasolutions.com/items/?x-ic-credential=xyz", function(data) {
    // Get the options for your select box
    var options = $("selector-for-your-select-box")[0].options;

    // Clear any old ones
    options.length = 0;

    // Add the new ones
    data.items.forEach(function(item) {
        options.add(new Option(item.ia_itemid));
    });
});