小冯的手写一个系列1（new/call/apply/bind/instanceof/reduce）

1. 不加注释了，大家自己阅读，都掌握了的请移步大厂。

2. 手写一个new：

   function _new(fn, ...args) {
         
         
       const obj = Object.create(fn.prototype)
       const ret = fn.apply(obj, args)
       return ret instanceof Object ? ret : obj
   }
   

3. 手写一个call：

   Function.prototype._call = function (context, ...args) {
         
         
       let context = context || window
       context.fn = this
       const res = context.fn(...args)
       delete context.fn
       return res
   }
   

4. 手写一个apply：

   Function.prototype._apply = function (context, arr) {
         
         
       let context = context || window
       context.fn = this
       let res
       if (!arr) {
         
         
          res = context.fn() 
       } else {
         
         
          res = context.fn(...arr)
       }
       delete context.fn
       return res
   }
   

5. 手写一个bind：

   Function.prototype._bind = function (context, ...args) {
         
         
       let self = this
       return function (...rest) {
         
         
           return self.apply(context, [...rest, ...args])
       }
   }
   

6. 手写一个instanceof：

   function _instanceof(left, right) {
         
         
       let right = right.prototype
       let left = left.__proto__
       while(true){
         
         
           if (left === null) {
         
         
   			return false
           }
           if (left === right) {
         
         
               return true
           }
           left = left.__proto__
       }
   }
   

7. 手写一个reduce：

   Array.prototype._reduce = function(fn, value) {
         
         
       const arr = this
       let acc = value || array[0]
       const startIndex = value ? 0 : 1
       for (let i = startIndex; i<arr.length; i++) {
         
         
           acc = fn(acc, arr[i], i, arr)
       }
       return acc
   }