How to get specific key counts that are serials

There is a dynamic object with the item_description_ key suffix index. In addition to these keys, there are other different keys.

const input = {
  ...
  item_description_1: "1"
  item_description_2: "2"
  item_description_3: "3"
  ...
}

How can I get the counts of the item_description_ keys? Expected result should be 3 in the above example.

Answer

You can use Object.keys to get all the keys of the object into the array; then filter on the key starting with item_description and count the length of the resultant array:

const input = {
  another_key: 'x',
  item_description_1: "1",
  item_description_2: "2",
  item_description_3: "3",
  something_else: 4
}

const cnt = Object.keys(input)
  .filter(v => v.startsWith('item_description'))
  .length;

console.log(cnt);

If your browser doesn’t support startsWith, you can always use a regex e.g.

.filter(v => v.match(/^item_description/))