Implement Array.prototype.map

You are required to implement a custom Array.prototype.map method, which is used to create a new array by applying a given callback function to every element of an original array. This method is particularly useful for transforming data.

Example:

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

const squaredNums = numbers.map((number) => {
  return number * number;
});

console.log(squaredNums); // Output: [1, 4, 9, 16, 25]

Solution

• Start by extending the Array.prototype to add the myMap function. This makes myMap available to all instances of arrays in your code.
• Define the myMap function. The myMap function should take a callback function (cb) as its argument. This callback function will be applied to each element of the array.
• Inside myMap, initialize an empty array named result. This array will store the results of applying the callback function to each array element.
• Use a for loop to iterate over each element of the array (this). The this keyword refers to the array on which myMap is called.
  • In each iteration, apply the callback function to the current element, its index, and the entire array (cb(this[i], i, this)).
• Push the result of the callback function into the result array.
• After the loop completes, return the result array. This array contains the transformed elements.

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

// Usage
const arr = [1, 2, 3, 4, 5];
const res = arr.myMap((item) => {
  return item * 2;
});

console.log(res); // 1, 4, 6, 8, 10

Where:

• cb is a callback function
• this[i] is a current item of an array
• this is a given array

Complexity:

• Time complexity: O(N)
• Space complexity: O(N)