Adding object properties into a JSON object

Question

I have a JSON object in this format.

[
    {
        "name": "schoolname",
        "line id": "0",
        "time": "4-5",
        "minage": "15",
        "maxage": "35"
    },
    {
        "name": "studentname1",
        "line id": "1",
        "class": "A"
    },
    {
        "name": "studentname2",
        "line id": "2",
        "class": "B"
    }
]

What I want to do

From a set of specified headers, get it from the "line id" : "0" and set it to the other items.

For Example: headers = ["time", "minage", "maxage"]

I get these from the "line id" : "0" and give it to others like this.

[
    {
        "name": "schoolname",
        "line id": "0",
        "time": "4-5",
        "minage": "15",
        "maxage": "35"
    },
    {
        "name": "studentname1",
        "line id": "1",
        "class": "A",
        "time": "4-5",
        "minage": "15",
        "maxage": "35"
    },
    {
        "name": "studentname2",
        "line id": "2",
        "class": "B",
        "time": "4-5",
        "minage": "15",
        "maxage": "35"
    }
]

and then remove the element with "line id" : "0", like this:

[
    {
        "name": "studentname1",
        "line id": "1",
        "class": "A",
        "time": "4-5",
        "minage": "15",
        "maxage": "35"
    },
    {
        "name": "studentname2",
        "line id": "2",
        "class": "B",
        "time": "4-5",
        "minage": "15",
        "maxage": "35"
    }
]

It is said that the 1st element would be a "line id" : "0".

What I've tried:

var headers = ["time", "minage", "maxage"]
var data = 
    [
        {
            "name": "schoolname",
            "line id": "0",
            "time": "4-5",
            "minage": "15",
            "maxage": "35"
        },
        {
            "name": "studentname1",
            "line id": "1",
            "class": "A"
        },
        {
            "name": "studentname2",
            "line id": "2",
            "class": "B"
        }
    ];

for(var i = 1; i < data.length; i++)//iterate over the data leaving the 1st line
{
    for(var j = 0; j < headers.length; j++)//add each header to the data lines
     {
        data[i][headers[j]] = data[0][headers[j]];
     }
}
data.splice(0,1);

Everything works fine and as intended. Is there a way to reduce the time-complexity of this and make it more efficient.

This now has a time complexity of O(n * m).

Is there a way around of adding these few objects to all the elements? As the key value pairs to be added for all the entries remain the same.

Answer 1

You can use Object.defineProperties like

var arr = [{
    "name": "schoolname",
    "line id": "0",
    "time": "4-5",
    "minage": "15",
    "maxage": "35"
  }, {
    "name": "studentname1",
    "line id": "1",
    "class": "A"
  }, {
    "name": "studentname2",
    "line id": "2",
    "class": "B"
  }],
  headers = ["time", "minage", "maxage"];


function addHeaders(arr, headers) {
  var header = arr.splice(0, 1)[0],
    propObj = headers.reduce(function(acc, el) {
      acc[el] = {
        value: header[el],
        writable: true,
        enumerable: true
      };
      return acc;
    }, {});

  for (var i = 0, len = arr.length; i < len; i++) {
    Object.defineProperties(arr[i], propObj);
  }
  return arr;
}

document.getElementById('r').innerHTML = 'initial: ' + JSON.stringify(arr,null,2) + '<br/>';
document.getElementById('r').innerHTML += 'result: ' + JSON.stringify(addHeaders(arr, headers),null,2);

<pre id="r"></pre>