Check out example codes for "typescript count array condition". It will help you in understanding the concepts better.

Code Example 1

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)

Code Example 2

var lengths = chars.map(function(word){
 return word.length
})

Code Example 3

var words = ['Hello', 'world'];

var lengths = words.map(function(word) {
  return word + ' = ' + word.length;
});

console.log(lengths);

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