Q112- Implement your own version of Array.prototype.map() in JavaScript

We can create a custom map function that works like the native Array.prototype.map(). It takes a callback function, applies it to each element, and returns a new array.

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1️⃣ Using a function on the prototype

// Custom map function
Array.prototype.myMap = function(callback) {
  const result = [];
  for (let i = 0; i < this.length; i++) {
    result.push(callback(this[i], i, this));
  }
  return result;
};

// Example usage
const numbers = [1, 2, 3, 4];
const doubled = numbers.myMap((num) => num * 2);

console.log(doubled); // [2, 4, 6, 8]

Explanation:

• this refers to the array on which myMap is called
• callback(this[i], i, this) passes:
  1. Current element
  2. Index
  3. Original array
• Push result into a new array → ensures immutability

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2️⃣ Using a standalone function (without modifying prototype)

function myMap(arr, callback) {
  const result = [];
  for (let i = 0; i < arr.length; i++) {
    result.push(callback(arr[i], i, arr));
  }
  return result;
}

// Example
const numbers = [5, 10, 15];
const squared = myMap(numbers, (n) => n * n);

console.log(squared); // [25, 100, 225]

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⚡ Key Points:

• Always return a new array, do not mutate the original
• Callback receives value, index, and array like native map()
• Works with all array types