How to implement a filter() for Objects in JavaScript ?

In this article, we will learn how to implement a filter() for Objects in JavaScript. In JavaScript, the filter() method is a built-in function for the array, not for the object. The filter() method outputs all the element of an array that pass a specific test or satisfies a specific function. The return type of the filter() method is an array that consists of all the elements for which function callback returned true. But for the object, we have to build a custom filter() method.

Below are the methods for implementing filter() for Objects in JavaScript:

• Using for loop and filter() Methods
• Using Object.entries() and Object.fromEntries() Method

Approach 1: Using for loop and filter() Methods

Example: The example returns IT department employees with the help of the filter() method.

javascript

let employees = [
    { name: "Tony Stark", department: "IT" },
    { name: "Peter Parker", department: "Pizza Delivery" },
    { name: "Bruce Wayne", department: "IT" },
    { name: "Clark Kent", department: "Editing" }
];

let output = employees.filter(employee => employee.department == "IT");
for (let i = 0; i < output.length; i++) {
    console.log(output[i].name)
};

Output

Tony Stark
Bruce Wayne

Approach 2: Using Object.entries() and Object.fromEntries() Method

In this method we will create custom built-in function for filtering the object.

Example:

Javascript

let employees = [
  { name: "Tony Stark", id: 1, department: "IT" },
  { name: "Peter Parker", id: 2, department: "Pizza Delivery" },
  { name: "Bruce Wayne", id: 3, department: "IT" },
  { name: "Clark Kent", id: 4, department: "Editing" }
];

Object.filter = (obj, predicate) =>
  Object.fromEntries(Object.entries(obj).
                     filter(([key, value]) =>
                     predicate(value)));

let filtered =
    Object.filter(employees, employee =>
                  employee.department === "IT");
console.log(filtered);

Output

{
  '0': { name: 'Tony Stark', id: 1, department: 'IT' },
  '2': { name: 'Bruce Wayne', id: 3, department: 'IT' }
}