JavaScript: remove all but 1 key from an object

Question

I have an object and I want to remove all values except the one that matches a particular key. For example, I could do this:

function remove(obj, key) {
  var value = obj[key]
  var ret = {}
  ret[key] = obj[key]
  obj = ret
}

Or I could iterate:

for (var k in obj) {
  if (k != key) {
    delete obj[k]
  }
}

But I'm wondering if there's a better way. Creating a temporary variable and iterating over the entire object both seem unnecessary. My initial attempt was:

obj = {
  key: obj[key]
}

But that resulted in an object with a key of key.

Try `[key]: obj[key]`. You need a computed property, not a literal property here. — Sebastian Simon, Oct 03 '17 at 13:46
@saniales thats what I tried initially and it didn't work. read the end of the question — ewok, Oct 03 '17 at 13:46

score 1 · Answer 1 · answered Oct 03 '17 at 13:51

1

You can indeed achieve what you described without using temporary variables.

function remove(obj, key) {
  return Object.assign({}, { [key] : obj[key]});
}

answered Oct 03 '17 at 13:51

kharhys

257
1
3

Timmetje · Answer 2 · 2017-10-03T14:02:51.957

0

You can just create a new object with [key]:obj[key].

var obj = {
 "a":1,
 "b":2
};
var key = "a";

function filterByKey(object, key) {
    return Object.create({[key]:obj[key]});
}
function filterByKey2(object, key) {
    return {[key]:obj[key]};
}
console.log(filterByKey(obj, key));
console.log(filterByKey2(obj, key));

edited Oct 03 '17 at 14:02

answered Oct 03 '17 at 13:56

Timmetje

7,641
18
36

JavaScript: remove all but 1 key from an object

2 Answers2