🔗LC2620 🟢 Easy 🧩 Pattern – Closures
📅 Day 2/30 Days of JavaScript
Given an integer n, return a counter function. This counter function initially returns n and then returns 1 more than the previous value every subsequent time it is called (n, n + 1, n + 2, etc).
Example
Input:
n = 10
["call","call","call"]
Output: [10,11,12]
Explanation:
counter() = 10 // The first time counter() is called, it returns n.
counter() = 11 // Returns 1 more than the previous time.
counter() = 12 // Returns 1 more than the previous time.Solution
In JavaScript, when functions are nested, the inner function forms a closure with the outer function. This means that the inner function retains access to the outer function’s lexical scope — essentially, the variables and definitions available at the time of its creation.
This behaviour allows us to manipulate and maintain state across multiple invocations of the inner function. In the solution below, we can keep incrementing the argument passed.
/**
* @param {number} n
* @return {Function} counter
*/
var createCounter = function (n) {
return () => n++
};
/**
* const counter = createCounter(10)
* counter() // 10
* counter() // 11
* counter() // 12
*/