Adding elements to array inside for.. in

Question

I'm trying to make a 2 dimensional array with a json data. The first array is made within a for in loop and is pushed to the top-level array after. I tried to print the array and I got same value for each elements which is the last data from the json.

json:

[
  {
    "startYear": 2014,
    "startMonth": 6,
    "startDay": 31,
    "endYear": 2014,
    "endMonth": 7,
    "endDay": 29,
    "selectedDate": "2014_7_8",
    "departureStation": "Manila",
    "arrivalStation": "Boracay (Caticlan)",
    "departureStationCode": "(MNL)",
    "arrivalStationCode": "(MPH)",
    "departureLabel": "DEPARTURE",
    "arrivalLabel": "RETURN",
    "dateMarketHash": {
      "date_0_2014_6_31": {
        "containerId": "date_0_2014_6_31",
        "fromLabel": "From",
        "currency": "PHP",
        "price": null,
        "formattedDate": "Thu, Jul 31, 2014", //data to get
        "year": "2014",
        "month": "6",
        "day": "31",
        "points": null,
        "pointsSuffix": "",
        "pointsLabelAppend": ""
      },
      "date_0_2014_7_1": {
        "containerId": "date_0_2014_7_1",
        "fromLabel": "From",
        "currency": "PHP",
        "price": 1929,
        "formattedDate": "Fri, Aug 01, 2014", //data to get
        "year": "2014",
        "month": "7",
        "day": "1",
        "points": 0,
        "pointsSuffix": "",
        "pointsLabelAppend": ""
      }
    }
  },
  {
    "startYear": 2014,
    "startMonth": 7,
    "startDay": 24,
    "endYear": 2014,
    "endMonth": 8,
    "endDay": 23,
    "selectedDate": "2014_8_8",
    "departureStation": "Boracay (Caticlan)",
    "arrivalStation": "Manila",
    "departureStationCode": "(MPH)",
    "arrivalStationCode": "(MNL)",
    "departureLabel": "DEPARTURE",
    "arrivalLabel": "RETURN",
    "dateMarketHash": {
      "date_1_2014_7_24": {
        "containerId": "date_1_2014_7_24",
        "fromLabel": "From",
        "currency": "PHP",
        "price": 3079,
        "formattedDate": "Sun, Aug 24, 2014",
        "year": "2014",
        "month": "7",
        "day": "24",
        "points": 0,
        "pointsSuffix": "",
        "pointsLabelAppend": ""
      },
      "date_1_2014_7_25": {
        "containerId": "date_1_2014_7_25",
        "fromLabel": "From",
        "currency": "PHP",
        "price": 3079,
        "formattedDate": "Mon, Aug 25, 2014",
        "year": "2014",
        "month": "7",
        "day": "25",
        "points": 0,
        "pointsSuffix": "",
        "pointsLabelAppend": ""
      }
    }
  }
]

code:

var current = json[0].dateMarketHash;
var top = [];
var array = [];
for(var key in current){
    top[0] = current[key].formattedDate;
    top[1] = current[key].currency;
    top[2] = current[key].price;
    array.push(top);
}       

document.write(array[0][0]); //prints "Fri, Aug 01, 2014" instead of "Thu, Jul 31, 2014"
document.write(array[1][0]); //prints "Fri, Aug 01, 2014"

@beautifulcoder the problem is right there in the comments of the last code block — php_nub_qq, Jul 31 '14 at 18:07
You change the value of top everytime, you should create a new top everytime — Marco Acierno, Jul 31 '14 at 18:07
even if i place "var top=[]" inside the loop, it prints the same — dgzz, Jul 31 '14 at 18:08
possible duplicate of [JavaScript closure inside loops – simple practical example](http://stackoverflow.com/questions/750486/javascript-closure-inside-loops-simple-practical-example) -- place both `top` and `key` inside their own closure — blgt, Jul 31 '14 at 18:14
can't grasp the concept of closure easily, how do i do that? — dgzz, Jul 31 '14 at 18:34

score 0 · Answer 1 · answered Jul 31 '14 at 18:16

0

Place "var top=[]" inside the loop and change array.push(top) to array.unshift(top), unshift method always insert element to the index 0.

answered Jul 31 '14 at 18:16

Allen

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php_nub_qq · Accepted Answer · 2014-07-31T18:46:49.550

It is because you initialize top outside the loop scope and that makes top[0] overwrite all references to the top array, which are being held in array

Put the top declaration inside the loop and see the difference

var current = json[0].dateMarketHash;
var array = [];
for(var key in current){
    var top = [];
    top[0] = current[key].formattedDate;
    top[1] = current[key].currency;
    top[2] = current[key].price;
    array[array.length] = top;
}

http://jsfiddle.net/sUpC8/

If you insist on top being outside the loop scope you can work-around this problem by cloning the top array

var current = json[0].dateMarketHash;
var array = [];
var top = [];
for(var key in current){
    top[0] = current[key].formattedDate;
    top[1] = current[key].currency;
    top[2] = current[key].price;
    array[array.length] = top.slice(0);
}

@DanielJohnGomez it prints correct values, did you even see the fiddle? — php_nub_qq, Jul 31 '14 at 18:38

Adding elements to array inside for.. in

2 Answers2