SOURCE

const feature = {
   "featureName":{
       "featureData":[
           {
               "count":11,
               "tm":11
           },
           {    
               "count":22,
               "tm":22
           }
       ],
       "nameToIndexMap":{
           "count": 0,
           "tm":1

       }
   }
};
const params = {
   "blue_test_pv_cid_list":{
       "featureData":[
           {
               "count":33,"tm":33
           },
           {
               "count":44,"tm":44
           },
       ]
   }};

var data = new Map();
var featureName=feature.featureName;
var featureData=featureName.featureData;
var length=featureData.length;
if (params instanceof Object && params.blue_test_pv_cid_list instanceof Object) {
    var params_featureData=params.blue_test_pv_cid_list.featureData;
    for(var key in params_featureData) {
        featureData[length++]=params_featureData[key];
    }
    
};
data=featureName;
console.log(data);