ArrayPollyfiils.js

const arr = [1, 2, 3, 4, 5, 6];

Array.prototype.myforEach = function (callback) {
  for (let i = 0; i < this.length; i++) {
    callback(this[i], i, this);
  }
};

arr.myforEach((val) => {
  console.log(val);
});

arr.map((val) => {
  return val * 2;
});

Array.prototype.myMap = function (callback) {
  const modifiedArray = new Array(this.length);
  for (let i = 0; i < this.length; i++) {
    modifiedArray[i] = callback(this[i], i, this);
  }
  return modifiedArray;
};

arr.filter((val) => {
  return val % 2 == 0;
});

Array.prototype.myFilter = function (callback, thisArg) {
  let arr = [];
  for (let i = 0; i < this.length; i++) {
    if (callback.call(thisArg, this[i], i, this)) {
      arr.push(this[i]);
    }
  }
  return arr;
};

// arr.reduce((),10)

Array.prototype.myReduce = function (callback, intialValue) {
  let value = intialValue;
  for (let i = 0; i < this.length; i++) {
    value = callback.call(this, value, this[i], i, this);
  }
  return value;
};

const res = arr.myReduce((prevVal, val) => {
  return prevVal + val;
}, 0);

console.log(res);