手写【map，forEach， filter，some，every， reduce，reduceRight】数组遍历方法

const arr = [1, 2, 3];
const obj = { a: 1 };

/**
 * map
 */
Array.prototype.myMap = function (cb) {
  // 调用者
  const _arr = this;
  // this指向
  const _arg2 = arguments[1] || window;
  const _length = _arr.length;
  let res = [];

  for (let i = 0; i < _length; i++) {
    res.push(cb.apply(_arg2, [_arr[i], i, _arr]));
  }
  return res;
};

/**
 * forEach
 */
Array.prototype.myForEach = function (cb) {
  const _arr = this;
  const _arg2 = arguments[1] || window;
  const _length = _arr.length;

  for (let i = 0; i < _length; i++) {
    cb.apply(_arg2, [_arr[i], i, _arr]);
  }
};

/**
 * filter
 */
Array.prototype.myFilter = function (cb) {
  const _arr = this;
  const _arg2 = arguments[1] || window;
  const _length = _arr.length;
  let res = [];

  for (let i = 0; i < _length; i++) {
    if (cb.apply(_arg2, [_arr[i], i, _arr])) {
      res.push(_arr[i]);
    }
  }
  return res;
};

/**
 * some
 * * 返回true | false
 */
Array.prototype.mySome = function (cb) {
  const _arr = this;
  const _arg2 = arguments[1] || window;
  const _length = _arr.length;
  let res = false;

  for (let i = 0; i < _length; i++) {
    if (cb.apply(_arg2, [_arr[i], i, _arr])) {
      res = true;
      break;
    }
  }
  return res;
};

/**
 * every
 * * 返回true | false
 */
Array.prototype.myEvery = function (cb) {
  const _arr = this;
  const _arg2 = arguments[1] || window;
  const _length = _arr.length;
  let res = true;

  for (let i = 0; i < _length; i++) {
    if (!cb.apply(_arg2, [_arr[i], i, _arr])) {
      res = false;
      break;
    }
  }
  return res;
};

/**
 * reduce
 * this一直指向window
 * 手动实现this指向
 */

Array.prototype.myReduce = function (cb, initialValue) {
  const _arr = this;
  const _arg2 = arguments[2] || window;
  const _length = _arr.length;

  for (let i = 0; i < _length; i++) {
    initialValue = cb.apply(_arg2, [initialValue, _arr[i], i, _arr]);
  }
  return initialValue;
};

/**
 * reduceRight
 * this一直指向window
 * 手动实现this指向
 */

Array.prototype.myReduceRight = function (cb, initialValue) {
  const _arr = this;
  const _arg2 = arguments[2] || window;
  const _length = _arr.length;

  for (let i = _length - 1; i >= 0; i--) {
    initialValue = cb.apply(_arg2, [initialValue, _arr[i], i, _arr]);
  }
  return initialValue;
};