手写数组方法foreach，myMap，myFilter，myFind，myEvery，mySome方法

1.myForeach

let arr = ['a', 'b', 'c', 'd', 'e', 'f', 100]
Array.prototype.myForeach = function (fn) {
    //    如果不是函数 抛异常
    if (!Object.prototype.toString.call(fn) == '[object Function]') {
        throw new Error(`${fn} is no a function`)
    }
    let param = this
    for (var i = 0; i < param.length; i++) {
        fn(param[i], i, param)
     }
    }
      arr.myForeach((item, index, param) => {
    console.log(item, index, param)
    return (arr[index])
     })
     console.log(arr)

2.myMap

let arr = [134, 134, 14, 134, 134, 123, 100]
// map : 映射，遍历数组并且返回一个新的数组
Array.prototype.myMap = function (fn) {
    // 如果不是函数 抛错
    if (!Object.prototype.toString.call(fn) == '[object Function]') {
        return new Error(`${fn} is no a function`)
    }
    var param = this
    var paramArray = []
    for (var i = 0; i < param.length; i++) {
        // 调用返回的每一项都放到新数组中
        paramArray.push(fn(param[i], i, param))
    }
    // 返回新数组
    return paramArray
}
let newArray = arr.myMap((item, index) => {
    return item+1
})
console.log(newArray)

3.myFilter

let arr = [134, 134, 14, 134, 134, 123, 100]
Array.prototype.myFilter = function (fn) {
// filter: 返回满足条件的每一项到新数组
if (!Object.prototype.toString.call(fn) == '[object Function]') {
        return new Error(`${fn} is no a function`)
    }
    let param  = this
    let newArray = []
    for (var i = 0; i < param.length; i++) {
        if (fn(param[i], i, param)) {
        	newArray.push(param[i])
        }
    }
    return newArray
}
let filterArray = arr.myFilter((item) => {
    return item == '100'
})
console.log(filterArray)

4.myFind，没有返回undefined

let arr = [134, 134, 14, 134, 134, 1230, 100]
	// find: 返回满足条件的第一个元素
	Array.prototype.myFind = function (fn) {
		if (typeof fn != 'function') {
			return new Error(`${fn} is no a function`)
		}
		let param = this
		for (var i = 0; i < param.length; i++) {
			if (fn(param[i], i, param)) {
				// 如果当前元素满足，则返回此元素
				return param[i]
			}
		}
	}
	let findArray = arr.myFind((item) => {
		return item > 134
	})
	console.log(findArray)

5.myEvery

let arr = [134, 134, 14, 134, 134, 1230, 100]
	// every: 判断数组中每一项是否满足条件 如有是返回true 否则返回false
	Array.prototype.myEvery = function (fn) {
		if (typeof fn != 'function') {
			return new Error(`${fn} is no a function`)
		}
		let param = this
		for (var i = 0; i < param.length; i++) {
			if (!fn(param[i], i, param)) {
				// 如果当前元素满足，则返回此元素
				return false
			}
		}
        // 否则返回true（循环遍历已经完成，没有为false的）
		return true
	}
	let everyArray = arr.myEvery((item) => {
		return item > 10
	})
	console.log(everyArray)

**6.mySome **

let arr = [134, 134, 14, 134, 134, 1230, 100]
	// some: 判断数组中是否有一项满足条件，如果有返回true，否则返回false
	Array.prototype.mySome = function (fn) {
		if (typeof fn != 'function') {
			return new Error(`${fn} is no a function`)
		}
		let param = this
		for (var i = 0; i < param.length; i++) {
			if (!fn(param[i], i, param)) {
				// 如果当前元素满足，则返回此元素
				return true
			}
		}
		return false
	}
	let SomeArray = arr.mySome((item) => {
		return item > 100000
	})
	console.log(SomeArray)