Handmade Array.prototype.filter()

custom_filter.js

const _arr = [
  { name: 'Mark', age: 21 },
  { name: 'Dan', age: 22 },
  { name: 'Zoe', age: 29 },
  { name: 'Victor', age: 21 },
  { name: 'Martin', age: 21 }
];

const filtered = _arr.filter(i => i.age === 21 );

const paramFunc = i => i.age === 21;

function customFilter(arr, callback, thisArg) {
  let results = [];
  
  for (let i = 0; i < arr.length; i++) {
    if (callback.call(thisArg, arr[i])) {
      results.push(arr[i]);
    }
  }
  
  return results;
};