How to count all objects in an array that match a condition?

Question

How can I count all objects in an array that match a condition: is_read == true?

This is how my array looks like:

[
  {
    "id": 1,
    "is_read": true,
  },
  {
    "id": 2,
    "is_read": true,
  },
  {
    "id": 3,
    "is_read": false,
  },
  {
    "id": 4,
    "is_read": true,
  },
]

Answer 1

Just use filter method by passing a callback function and use length property applied for the result of filtering.

let data = [ { "id": 1, "is_read": true, }, { "id": 2, "is_read": true, }, { "id": 3, "is_read": false, }, { "id": 4, "is_read": true, }, ],
length = data.filter(function(item){
  return item.is_read;
}).length;
console.log(length);

You can also use a lambda expression.

 let data = [ { "id": 1, "is_read": true, }, { "id": 2, "is_read": true, }, { "id": 3, "is_read": false, }, { "id": 4, "is_read": true, }, ],
length = data.filter(d => d.is_read).length;
console.log(length);