實作JS的method理解原理

Array.prototype.myReduce = function (callback, initialValue) {
  let acc = initialValue === undefined ? this[0] : initialValue;
  this.forEach((element) => {
    acc = callback(acc, element);
  });
  return acc;
};

console.log([1, 2, 3].myReduce((acc, n) => acc + n, 1000));

Array.prototype.myMap = function (callback) {
  let result = [];
  this.forEach((n, i) => {
    result.push(callback(n, i));
  });
  return result;
};

console.log([1, 2, 3].myMap((n, i) => n * 3));
console.log(Array.prototype.myMap.call([1, 2, 3], (n, i) => n * 10));