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)

Implement Array.prototype.map

Solution​

Solution