Recursively remove null values from JavaScript object

Question

I have a JSON obj, after some operations (like delete some pieces), I print it and everything looks good except that I have some null values. How do I remove th

Answer 1

// Iterate the array from back to front, removing null entries
for (var i=obj.store.book.length;i--;){
  if (obj.store.book[i]===null) obj.store.book.splice(i,1);
}

If you want to remove all null values recursively from both objects and arrays:

// Compact arrays with null entries; delete keys from objects with null value
function removeNulls(obj){
  var isArray = obj instanceof Array;
  for (var k in obj){
    if (obj[k]===null) isArray ? obj.splice(k,1) : delete obj[k];
    else if (typeof obj[k]=="object") removeNulls(obj[k]);
  }
}

Seen in action:

var o = {
  "store": {
    "book": [
       null,
       {
         "category": "fiction",
         "author": "Evelyn Waugh",
         "title": "Sword of Honour",
         "price": 12.99
       },
       null,
       {
          "category": "fiction",
          "author": "J. R. R. Tolkien",
          "title": "The Lord of the Rings",
          "isbn": "0-395-19395-8",
          "price": 22.99
       }
    ],
    "bicycle": {
       "color": "red",
       "bad": null,
       "price": 19.95
    }
  }
}

removeNulls(o);

console.log(JSON.stringify(o,null,2));
// {
//   "store": {
//     "book": [
//       {
//         "category": "fiction",
//         "author": "Evelyn Waugh",
//         "title": "Sword of Honour",
//         "price": 12.99
//       },
//       {
//         "category": "fiction",
//         "author": "J. R. R. Tolkien",
//         "title": "The Lord of the Rings",
//         "isbn": "0-395-19395-8",
//         "price": 22.99
//       }
//     ],
//     "bicycle": {
//       "color": "red",
//       "price": 19.95
//     }
//   }
// }