Array.prototype.lForEach = function (callback, thisArg) {
  if (typeof callback !== 'function') {
    throw new TypeError(`${callback} must be a function`);
  }
  const array = this;
  for (let i = 0; i < array.length; i++) {
    // 判断对象本身(非原型链)是否含有该属性
    if (array.hasOwnProperty(i)) {
      callback.call(thisArg, array[i], i, array);
    }
  }
};

Array.prototype.lMap = function (callback, thisArg) {
  if (typeof callback !== 'function') {
    throw new TypeError(`${callback} must be a function`);
  }

  const array = this;
  const resArr = new Array(array.length);

  for (let i = 0; i < array.length; i++) {
    if (array.hasOwnProperty(i)) {
      const res = callback.call(thisArg, array[i], i, array);
      resArr[i] = res;
    }
  }
  return resArr;
};

Array.prototype.lFilter = function (callback, thisArg) {
  if (typeof callback !== 'function') {
    throw new TypeError(`${callback} must be a function`);
  }

  const array = this;
  const resArr = new Array();
  let n = 0;
  for (let i = 0; i < array.length; i++) {
    if (array.hasOwnProperty(i)) {
      const flag = callback.call(thisArg, array[i], i, array);
      if (flag) {
        resArr[n] = array[i];
        n++;
      }
    }
  }
  return resArr;
};

Array.prototype.lReduce = function (callback, initialValue) {
  if (typeof callback !== 'function') {
    throw new TypeError(`${callback} must be a function`);
  }
  if (this.length === 0 && initialValue === undefined) {
    throw new TypeError('Reduce of empty array with no initial value');
  }

  // 初始化累加器和起始索引
  let accumulator = initialValue !== undefined ? initialValue : this[0];
  let startIdx = initialValue !== undefined ? 0 : 1;

  for (let i = startIdx; i < this.length; i++) {
    accumulator = callback(accumulator, this[i], i, this);
  }
  return accumulator;
};

Array.prototype.lFind = function (callback, thisArg) {
  if (typeof callback !== 'function') {
    throw new TypeError(`${callback} must be a function`);
  }

  const array = this;
  let target = null;
  for (let i = 0; i < array.length; i++) {
    if (array.hasOwnProperty(i)) {
      const flag = callback.call(thisArg, array[i], i, array);
      if (flag) {
        target = array[i];
        return target;
      }
    }
  }
  return undefined;
};

Array.prototype.lFlat = function (depth = 1) {
  if (typeof depth !== 'number') {
    throw new TypeError(`${depth} must be a number`);
  }
  let result = [];
  this.forEach((item) => {
    if (Array.isArray(item) && depth > 0) {
      result = result.concat(item.lFlat(depth === Infinity ? depth : depth - 1));
    } else {
      result.push(item);
    }
  });
  return result;
};