javascript always pushes the same object

Question

Do you have any idea why this code always adds the last object? Because I used

var obj = {}

and

var newBase = Object.assign({}, baseJson)

but code always use the same reference?

module.exports = (csv, baseJson) => {

var lines=csv.split("\n");

var result = [];

var headers=lines[0].split(";");
for(var i=1;i<lines.length;i++){
    var obj = {};
    var newBase = Object.assign({}, baseJson);
    obj["case"] = "Scenario";
    obj["request"] = newBase;
    obj["response"] = {
        responseCode: "5",
        actionCode: "0",
        approvalCode: "98765X",
    }
    var currentline=lines[i].split(";");
    var responseTags = ["responseCode", "actionCode", "approvalCode"];      
    for(var j=0;j<headers.length;j++){

        headers[j] = headers[j].replace('\r','');
        currentline[j] = currentline[j].replace('\r','')
        if (headers[j] == "Scenario") {
            obj["case"] = currentline[j];
        }
        else if (responseTags.indexOf(headers[j]) > -1 ){
            obj["response"][headers[j]] = currentline[j];
        }
        else {
            saveValue(obj["request"], headers[j], currentline[j]);
        }
    }
    result.push(obj);

}

I tried almost everything but I could not manage to create a new object. It uses the same reference. This code is in node.js. Thank you

What does `console.log(result)` after the loop finishes show? — Scott Marcus, Apr 06 '18 at 22:41
@ScottMarcus you are right problem is not about this part of code. Problem is in mocha. I try to use this array in a test but it uses last element always I will check it again. — Mehmet Kemal Bayer, Apr 06 '18 at 22:50
@MehmetKemalBayer, move var obj = {}; declaration out of for loop and declare before for loop — Naga Sai A, Apr 06 '18 at 22:56

Manivannan · Answer 1 · 2018-04-06T23:12:33.853

1

Object.assign may not clone inner objects and it just takes same reference, try stringify and parse it.

 var newBase = JSON.parse(JSON.stringify(baseJson));

Refer to know more : What is the most efficient way to deep clone an object in JavaScript?

edited Apr 06 '18 at 23:12

answered Apr 06 '18 at 23:06

Manivannan

3,074
3
21
32

score 0 · Accepted Answer · answered Apr 06 '18 at 22:59

0

This is because Javascript vars scoped to functions, not blocks. Effectively in your code obj is declared outside of the loop and it's properties mutated.

let should solve the problem:

for(var i=1;i<lines.length;i++){
  let obj = {};
  ...
  result.push(obj);
}

answered Apr 06 '18 at 22:59

Artem Koshelev

10,548
4
36
68

Thank you, the problem was about the other part of the code that calls the part I wrote above. I solved it by using let there. – Mehmet Kemal Bayer Apr 07 '18 at 08:03

javascript always pushes the same object

2 Answers2