带你读《现代Javascript高级教程》四、JavaScript数组（3）

// 模拟实现 forEach() 方法Array.prototype.myForEach = function(callbackFn) {
  for (let i = 0;
 i < this.length; i++) {
    callbackFn(this[i], i, this);
  }};
// 模拟实现 map() 方法Array.prototype.myMap = function(callbackFn) {
  const mappedArray = [];
  for (let i = 0; i < this.length; i++) {
    mappedArray.push(callbackFn(this[i], i, this));
  }
  return mappedArray;};
// 示例使用const myArray = [1, 2, 3];
myArray.myForEach((value, index) => {
  console.log(`Element at index indexis{index} is {value}`);});
const doubledArray = myArray.myMap(value => value * 2);
console.log(doubledArray);  // 输出：[2, 4, 6]

// 模拟实现 toString() 方法Array.prototype.myToString = function() {
  let result = '';
  for (let i = 0; i < this.length; i++) {
    if (i > 0) {
      result += ', ';
    }
    result += this[i];
  }
  return result;};
// 模拟实现 join() 方法Array.prototype.myJoin = function(separator = ',') {
  let result = '';
  for (let i = 0; i < this.length; i++) {
    if (i > 0) {
      result += separator;
    }
    result += this[i];
  }
  return result;};
// 示例使用const myArray = [1, 2, 3];
console.log(myArray.myToString());      // 输出：'1, 2, 3'
console.log(myArray.myJoin('-'));       // 输出：'1-2-3'

// 模拟实现 sort() 方法Array.prototype.mySort = function(compareFn) {
  const length = this.length;
  for (let i = 0; i < length - 1; i++) {
    for (let j = 0; j < length - 1 - i; j++) {
      if (compareFn(this[j], this[j + 1]) > 0) {
        [this[j], this[j + 1]] = [this[j + 1], this[j]];
      }
    }
  }
  return this;};
// 模拟实现 indexOf() 方法Array.prototype.myIndexOf = function(searchElement, fromIndex = 0) {
  const length = this.length;
  for (let i = Math.max(fromIndex, 0); i < length; i++) {
    if (this[i] === searchElement) {
      return i;
    }
  }
  return -1;};
// 示例使用const myArray = [5, 2, 1, 4, 3];
console.log(myArray.mySort());        // 输出：[1, 2, 3, 4, 5]
console.log(myArray.myIndexOf(4));  // 输出：3

// 模拟实现 isArray() 方法
Array.myIsArray = function(obj) {
  return Object.prototype.toString.call(obj) === '[object Array]';};
// 模拟实现 find() 方法Array.prototype.myFind = function(callbackFn) {
  for (let i = 0; i < this.length; i++) {
    if (callbackFn(this[i], i, this)) {
      return this[i];
    }
  }
  return undefined;};
// 示例使用const myArray = [1, 2, 3, 4, 5];
console.log(Array.myIsArray(myArray));    // 输出：true
console.log(myArray.myFind(value => value > 3)); // 输出：4