Category: Interview Questions

A closure is when a function remembers variables from its outer scope, even after the outer function has finished.

Example:

function outer() {
  let count = 0;
  return function inner() {
count++;
return count;
  };
}

let counter = outer();
console.log(counter()); // 1
console.log(counter()); // 2

Here, inner() remembers count from outer().

• == → loose equality, converts data types before comparison.
• === → strict equality, checks value and type.

Example:

console.log(5 == "5");  // true  (type conversion)
console.log(5 === "5"); // false (strict check)

• var → Function-scoped, can be redeclared. (Older way, avoid in modern JS)
• let → Block-scoped, can be updated but not redeclared in the same scope.
• const → Block-scoped, cannot be updated (immutable reference).

Example:

var x = 10; // function scoped
let y = 20; // block scoped
const z = 30; // constant