Closure Explained in JS

Nikita Maharana — Wed, 13 May 2026 08:53:12 +0000

Closure: An inner fxn remembers the outer fxn values even after outer fxn execution gets ended.

We use this in techniques called memorization it means making code able to remember the previous input and its corresponding output such that it will not again calculate for same input.

//CLosure
function outer(){
var x = 25;
function inner() {
x++;//x is not in inner fxn its in outer but it remembers outer value that called memorization or closure
console.log(x);
}
return inner;
}
let result = outer();
console.log(result);
//it calls outer and outer returns inner so whole innner fxn returns
//inner is not yet called so 26 will not be printed as it is seems

result();//inner called 26
result()//27
result()//28 and so on...

Callback Functions in JavaScript Explained

Nikita Maharana — Wed, 13 May 2026 08:22:18 +0000

Callback Functions

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

e.g. function kind(){
console.log("I'm kind");
}
function rude(){
console.log("I'm rude");
}
function fun(a, b){
a();//calls kind()
b();//calls rude()
}
fun(kind, rude);

//Output:
I'm kind
I'm rude

Here, kind and rude are callback functions because they are passed as arguments to another function named as fun.
And fun is called a higher order function because it accepts functions (kind and rude) as parameters.

DEV Community: Nikita Maharana

Closure Explained in JS

Callback Functions in JavaScript Explained

Callback Functions