What is Call Back Function? and Array Inbuilt method=> filter() ;

While learning JavaScript, I came across two important concepts: Callback Functions and the array filter() method.

At first, they looked confusing, but simple examples made them much easier to understand.

What is a Callback Function?

A callback function is a function that is passed as an argument to another function.

Example:

function greet(name, callback) {
  console.log("Hello " + name);
  callback();
}

function message() {
  console.log("Welcome to JavaScript!");
}

greet("Narasimma", message);

Here, message is passed to greet() as a callback function.

Simple Way to Remember 💡

A callback is simply a function given to another function to be called later.

What is filter()? 🔍

filter() is a JavaScript array method used to select elements that match a condition.

Example:

let numbers = [10, 15, 20, 25, 30];

let result = numbers.filter(function(number) {
  return number > 20;
});

console.log(result);

Output:

[25, 30]

The filter() method checks every element and keeps only the elements where the condition is true.

Using Arrow Function

We can write the same code in a shorter way:

let numbers = [10, 15, 20, 25, 30];

let result = numbers.filter(number => number > 20);

console.log(result);

filter() with Objects

We can also filter objects.

let students = [
  { name: "Arun", age: 20 },
  { name: "Kumar", age: 17 },
  { name: "Ravi", age: 22 }
];

let adults = students.filter(student => student.age >= 18);

console.log(adults);

This returns only the students whose age is 18 or above.

Callback + filter()

Now we can connect both concepts.

The function passed inside filter() is a callback function.

let numbers = [1, 2, 3, 4, 5];

let evenNumbers = numbers.filter(function(number) {
  return number % 2 === 0;
});

console.log(evenNumbers);

Output:

[2, 4]

So, filter() uses a callback function to check each array element.

Easy Way to Remember 🧠

Callback Function → A function passed to another function.

filter() → Selects elements based on a condition.

Array
↓
filter()
↓
Callback checks each item
↓
Condition true?
↓
Keep the item ✅

Conclusion

Today I learned that callback functions are an important part of JavaScript, and filter() is a very useful array method.

These concepts are especially useful when working with arrays, objects, APIs, and real-world JavaScript applications.

Learn → Practice → Build 🚀

javascript #webdev #beginners #coding