手寫模擬實現find，findIndex，some，every，map，filter，reduce

1. 模擬實現find

    let arrFind = [12,15,19]

    Array.prototype.myFind = function(fn) { //必須使用function不能使用箭頭函數，this指向調用的數組
     if(typeof fn != 'function'){
       throw TypeError('err function')
     }
     for(let i = 0; i < this.length; i++){
       if(fn(this[i])){
         return this[i]
       }
     }
     return undefined // 沒有匹配則返回undefined
   }
   
   let find = arrFind.myFind(item => { // 返回第一個判斷爲true的值
      return item > 12
    })
    console.log('find:'+find) // find:15

2. 模擬實現findIndex

    let arrFindIndex = [12,15,19]

    Array.prototype.myFindIndex = function(fn) { //必須使用function不能使用箭頭函數，this指向調用的數組
     if(typeof fn != 'function'){
       throw TypeError('err function')
     }
     for(let i = 0; i < this.length; i++){
       if(fn(this[i])){
         return i
       }
     }
     return undefined // 沒有匹配則返回undefined
   }
   
   let findIndex = arrFindIndex.myFindIndex(item => { // 返回第一個判斷爲true的值
      return item > 12
    })
    console.log('findIndex:'+findIndex) // findIndex:1

3. 模擬實現some

    let arrSome = [12,15,19]

    Array.prototype.mySome = function(fn) { //必須使用function不能使用箭頭函數，this指向調用的數組
      if(typeof fn != 'function'){
        throw new TypeError(`error ${fn} no a function `)
      }
      for (let i = 0; i < this.length; i++) {
        if(fn(this[i])){
          return true
        }
      }
      return false
    }

    let some = arrSome.mySome(item => {
      return item > 19 
    })
    console.log('some:'+some) // some:false

4. 模擬實現every

    let arrEvery = [12,15,19]

    Array.prototype.myEvery = function(fn) {
      if(typeof fn != 'function'){
        throw new TypeError(`error ${fn} no a function `)
      }
      for (let i = 0; i < this.length; i++) {
        if(!fn(this[i])){
          return false
        }
      }
      return true
    }

    let every = arrEvery.myEvery(item => {
      return item > 19 
    })
    console.log('every:'+every) // every:false

5. 模擬實現map

    let arrMap = [12,15,19]

    Array.prototype.myMap = function(fn) { //必須使用function不能使用箭頭函數，this指向調用的數組
      if(typeof fn != 'function'){
        throw new TypeError(`error ${fn} no a function `)
      }
      let arrayData = []
      for (let i = 0; i < this.length; i++) {
        if(fn(this[i])){
          arrayData.push(fn(this[i]))
        }
      }
      return arrayData;
    }

   let map = arrMap.map(item => {
     item += 3;
     return item + 'map'
   })
   console.log('map:'+map) // map:15map,18map,22map

6. 模擬實現filter

    let arrFilter = [12,15,19]

    Array.prototype.myFilter = function(fn) { //必須使用function不能使用箭頭函數，this指向調用的數組
      if(typeof fn != 'function'){
        throw new TypeError(`error ${fn} no a function `)
      }
      let arrayData = []
      for (let i = 0; i < this.length; i++) {
        if(fn(this[i])){
          arrayData.push(this[i])
        }
      }
      return arrayData;
    }

   let filter = arrFilter.myFilter(item => {
     return item > 12
   })
   console.log('filter:'+filter) // filter:15,19

7. 模擬實現reduce

   let arrReduce = [12,15,19]

   Array.prototype.myReduce = function(fn,obj) { //必須使用function不能使用箭頭函數，this指向調用的數組
    if(typeof fn != 'function'){
      throw new TypeError(`error ${fn} no a function `)
    }
    for (let i = 0; i < this.length; i++) {
        obj = fn(obj,this[i])
    }
    return obj
   }

   let reduce = arrReduce.myReduce((pre,item) => {
    pre = pre + item
     return pre
   },0)
   console.log('reduce:'+reduce) // reduce:46