Array.prototype.newMap = function(fn, context) {
    let newArr = new Array;
    if(typeof fn !== "function") {
        throw new TypeError(fn + "is not a function");
    }
    var context = arguments[1];
    for (var i = 0; i < this.length; i++) {
        newArr.push(fn.call(context, this[i], i, this))
    }
    return newArr
}

Array.prototype.newFind = function(fn, context) {
    let str;
    if(typeof fn !== "function") {
        throw new TypeError(fn + "is not a function");
    }
    var context = arguments[1];
    for (var i = 0; i < this.length; i++) {
        if(fn.call(context, this[i], i, this)) {str = this[i];break; }
    }
    return str
}

Array.prototype.newfilter = function (fn, context) {
    let newArr = new Array;
    if (typeof fn !== "function") {
        throw new TypeError(fn + "is not a function");
    }
    var context = arguments[1];
    for (var i = 0; i < this.length; i++) {
        if (fn.call(context, this[i], i, this)) { newArr.push(this[i]) }
    }
    return newArr
}

Array.prototype.myForEach = function(cb){ // 在Array对象的原型上添加 myForEach()方法， 接受一个回调函数
	for(let i=0; i<this.length; i++){ // this指的是当前实例化的数组对象
		let item = this[i]; // 定义回调函数接受的三个参数
		let index = i;
		let array = this;
		cb(item,index,array) // 调用
	}
}

Array.prototype.myMap = function(cb) {
	let newArr = []; // 定义一个新的数组，用来接受返回值
	for (let i = 0; i < this.length; i++) {
		let item = this[i];
		let index = i;
		let array = this;
		let result = cb(item, index, array);
		newArr.push(result) // 将回到函数的结果push到新的数组中
	}
	return newArr // 返回这个新的数组
}

Array.prototype.myFilter = function(cb) {  // 实现方法和map()方法差不多
	let newArr = [];
	for (var i = 0; i < this.length; i++) {
		let item = this[i];
		let index = i;
		let array = this;
		let result = cb(item, index, array); 
		if (result) { // 判断回调函数的结果否为true，为true则将 该项的item push到新的数组中
			newArr.push(item);
		}
	}
	return newArr; // 返回新的数组
}

Array.prototype.myEvery = function(cb){
	for (var i = 0; i < this.length; i++) {
		let item = this[i];
		let index = i;
		let array = this;
		let result = cb(item, index, array);
		if (!result) { // 当返回false时，怎停止遍历，返回false。
			return false; 
		}
	}
	return true;
}

Array.prototype.mySome = function() {
	for (var i = 0; i < this.length; i++) {
		let item = this[i];
		let index = i;
		let array = this;
		let result = cb(item, index, array);
		if (result) {
			return true; // 有一个通过了测试 则终止遍历，返回true
		}
	}
	return false; // 一个都没有通过测试，返回false
}

function map (arr, fun) {
  let res = []
  arr.forEach((...args) => {
    res.push(fun(...args))
  })
  return res
}

function filter (arr, fun) {
  let res = []
  arr.forEach((...args) => {
    if (fun(...args)) {
      res.push(args[0])
    }
  })
  return res
}

function find (arr, fun) {
  let res = undefined
  arr.some((...args) => {
    if (fun(...args)) {
      res = args[0]
      return true
    }
    return false
  })
  return res
}