angular.js

getNestedDataBetter: function (){
  //create your deferred promise.
  var deferred = $q.defer();
  
  //do your thing.
  $http.get('parents.json')
    .then(function(result){
      var parents = result.data;
      $http.get('children.json')
        .then(function(result) {
          var children = result.data;
            angular.forEach(parents, function(parent) {
              parent.children = [];            
              angular.forEach(children, function(child) {
                if(parent.childIds.indexOf(child.id) >= 0) {
                  parent.children.push(child);
                }
              });
            }); 
            
            //at whatever point in your code, you feel your
            // code has loaded all necessary data and/or
            // resolve your promise.
            deferred.resolve(parents);
        });
    });
    
  //return your promise to the user.
  return deferred.promise;
}