adding JSON object to JSON array at runtime issue

Question

simply I want to get value of a key at JSON object but at run time, this work at design time like this.

 var studentsData = [
            { "studentName": "Elen", "Birthyear": 1981 }
            , { "studentName": "Stev", "Birthyear": 1987 }];
console.log(studentsData[0].studentName); // print Elen

But if push object to the array at runtime like this

var studentsData = [];
var jsonObj={ "studentName": "Elen", "Birthyear": 1981 };  //because i intend to get the object data at runtime
studentsData.push(jsonObj);
console.log(studentsData[0].studentName);

by this way it give me error :Uncaught TypeError: Cannot read property 'studentName' of undefined
please help, THANK YOU

Sorry by mistake i put different array variable from another code, but it seems that My real problem from the start was the same non solved this problem :- How do I assign a variable from localForage as I do in localStorage?

You are trying to read `populationData` and not `studentsData`? — David S., Nov 10 '16 at 03:16
You need to clarify what language you are writing in. and add that in the tag as well. — GeneCode, Nov 10 '16 at 03:17
You have missed something. What is `populationData` in the first and second case? Since it works in case #1, show where and how declare it. — Yeldar Kurmangaliyev, Nov 10 '16 at 03:17
You've tagged your post "local-storage", but do not mention local storage. Does this question have something to do with local storage? Does it have something to do with JSON? — , Nov 10 '16 at 15:58

score 0 · Answer 1 · answered Nov 10 '16 at 03:57

You are accessing wrong variable. use studentsData instead:

var studentsData = [];
var jsonObj={ "studentName": "Elen", "Birthyear": 1981 };  //because i intend to get the object data at runtime
studentsData.push(jsonObj);
console.log(studentsData[0].studentName);

score 0 · Answer 2 · answered Nov 10 '16 at 04:55

0

console.log(studentsData[0].studentName);

Since you are adding the json object to studentsData array.

answered Nov 10 '16 at 04:55

Murad Ariff

11
2

score 0 · Accepted Answer · answered Nov 10 '16 at 10:00

try to read studentsData instead of populationData.

working demo :

using for in loop :

 var studentsData = [
            { "studentName": "Elen", "Birthyear": 1981 }
            , { "studentName": "Stev", "Birthyear": 1987 }];

for (var i in studentsData) {
  console.log(studentsData[i].studentName);
}

using Array map() function :

 var studentsData = [
            { "studentName": "Elen", "Birthyear": 1981 }
            , { "studentName": "Stev", "Birthyear": 1987 }];

var result = studentsData.map(function(elem) {
  return elem.studentName;
});

console.log(result);

adding JSON object to JSON array at runtime issue

3 Answers3