js实现Promise,call,apply,bind_promise is not callable

综述：手写一下，加深对知识的理解

1.原生js实现Promise?

 // 判断变量否为function
  const isFunction = variable => typeof variable === 'function'
  // 定义Promise的三种状态常量
  const PENDING = 'PENDING'
  const FULFILLED = 'FULFILLED'
  const REJECTED = 'REJECTED'
 
  class MyPromise {
    constructor (handle) {
      if (!isFunction(handle)) {
        throw new Error('MyPromise must accept a function as a parameter')
      }
      // 添加状态
      this._status = PENDING
      // 添加状态
      this._value = undefined
      // 添加成功回调函数队列
      this._fulfilledQueues = []
      // 添加失败回调函数队列
      this._rejectedQueues = []
      // 执行handle
      try {
        handle(this._resolve.bind(this), this._reject.bind(this)) 
      } catch (err) {
        this._reject(err)
      }
    }
    // 添加resovle时执行的函数
    _resolve (val) {
      const run = () => {
        if (this._status !== PENDING) return
        // 依次执行成功队列中的函数，并清空队列
        const runFulfilled = (value) => {
          let cb;
          while (cb = this._fulfilledQueues.shift()) {
            cb(value)
          }
        }
        // 依次执行失败队列中的函数，并清空队列
        const runRejected = (error) => {
          let cb;
          while (cb = this._rejectedQueues.shift()) {
            cb(error)
          }
        }
        /* 如果resolve的参数为Promise对象，则必须等待该Promise对象状态改变后,
          当前Promsie的状态才会改变，且状态取决于参数Promsie对象的状态
        */
        if (val instanceof MyPromise) {
          val.then(value => {
            this._value = value
            this._status = FULFILLED
            runFulfilled(value)
          }, err => {
            this._value = err
            this._status = REJECTED
            runRejected(err)
          })
        } else {
          this._value = val
          this._status = FULFILLED
          runFulfilled(val)
        }
      }
      // 为了支持同步的Promise，这里采用异步调用
      setTimeout(run, 0)
    }
    // 添加reject时执行的函数
    _reject (err) { 
      if (this._status !== PENDING) return
      // 依次执行失败队列中的函数，并清空队列
      const run = () => {
        this._status = REJECTED
        this._value = err
        let cb;
        while (cb = this._rejectedQueues.shift()) {
          cb(err)
        }
      }
      // 为了支持同步的Promise，这里采用异步调用
      setTimeout(run, 0)
    }
    // 添加then方法
    then (onFulfilled, onRejected) {
      const { _value, _status } = this
      // 返回一个新的Promise对象
      return new MyPromise((onFulfilledNext, onRejectedNext) => {
        // 封装一个成功时执行的函数
        let fulfilled = value => {
          try {
            if (!isFunction(onFulfilled)) {
              onFulfilledNext(value)
            } else {
              let res =  onFulfilled(value);
              if (res instanceof MyPromise) {
                // 如果当前回调函数返回MyPromise对象，必须等待其状态改变后在执行下一个回调
                res.then(onFulfilledNext, onRejectedNext)
              } else {
                //否则会将返回结果直接作为参数，传入下一个then的回调函数，并立即执行下一个then的回调函数
                onFulfilledNext(res)
              }
            }
          } catch (err) {
            // 如果函数执行出错，新的Promise对象的状态为失败
            onRejectedNext(err)
          }
        }
        // 封装一个失败时执行的函数
        let rejected = error => {
          try {
            if (!isFunction(onRejected)) {
              onRejectedNext(error)
            } else {
                let res = onRejected(error);
                if (res instanceof MyPromise) {
                  // 如果当前回调函数返回MyPromise对象，必须等待其状态改变后在执行下一个回调
                  res.then(onFulfilledNext, onRejectedNext)
                } else {
                  //否则会将返回结果直接作为参数，传入下一个then的回调函数，并立即执行下一个then的回调函数
                  onFulfilledNext(res)
                }
            }
          } catch (err) {
            // 如果函数执行出错，新的Promise对象的状态为失败
            onRejectedNext(err)
          }
        }
        switch (_status) {
          // 当状态为pending时，将then方法回调函数加入执行队列等待执行
          case PENDING:
            this._fulfilledQueues.push(fulfilled)
            this._rejectedQueues.push(rejected)
            break
          // 当状态已经改变时，立即执行对应的回调函数
          case FULFILLED:
            fulfilled(_value)
            break
          case REJECTED:
            rejected(_value)
            break
        }
      })
    }
    // 添加catch方法
    catch (onRejected) {
      return this.then(undefined, onRejected)
    }
    // 添加静态resolve方法
    static resolve (value) {
      // 如果参数是MyPromise实例，直接返回这个实例
      if (value instanceof MyPromise) return value
      return new MyPromise(resolve => resolve(value))
    }
    // 添加静态reject方法
    static reject (value) {
      return new MyPromise((resolve ,reject) => reject(value))
    }
    // 添加静态all方法
    static all (list) {
      return new MyPromise((resolve, reject) => {
        /**
         * 返回值的集合
         */
        let values = []
        let count = 0
        for (let [i, p] of list.entries()) {
          // 数组参数如果不是MyPromise实例，先调用MyPromise.resolve
          this.resolve(p).then(res => {
            values[i] = res
            count++
            // 所有状态都变成fulfilled时返回的MyPromise状态就变成fulfilled
            if (count === list.length) resolve(values)
          }, err => {
            // 有一个被rejected时返回的MyPromise状态就变成rejected
            reject(err)
          })
        }
      })
    }
    // 添加静态race方法
    static race (list) {
      return new MyPromise((resolve, reject) => {
        for (let p of list) {
          // 只要有一个实例率先改变状态，新的MyPromise的状态就跟着改变
          this.resolve(p).then(res => {
            resolve(res)
          }, err => {
            reject(err)
          })
        }
      })
    }
    finally (cb) {
      return this.then(
        value  => MyPromise.resolve(cb()).then(() => value),
        reason => MyPromise.resolve(cb()).then(() => { throw reason })
      );
    }
  }

2.js实现bind?

  
    Function.prototype.bind = function(oThis) {
      if (typeof this !== 'function') {
        // closest thing possible to the ECMAScript 5
        // internal IsCallable function
        throw new TypeError('Function.prototype.bind - what is trying to be bound is not callable');
      }
  ​
      var aArgs   = Array.prototype.slice.call(arguments, 1),
          fToBind = this,
          // 空函数
          fNOP    = function() {},
          fBound  = function() {
            return fToBind.apply(this instanceof fNOP
                   ? this
                   : oThis,
                   // 获取调用时(fBound)的传参.bind 返回的函数入参往往是这么传递的
                   aArgs.concat(Array.prototype.slice.call(arguments)));
          };
  ​
      // 维护原型关系
      if (this.prototype) {
        // Function.prototype doesn't have a prototype property
        fNOP.prototype = this.prototype; 
      }
      fBound.prototype = new fNOP();
  ​
      return fBound;
  };
  // 测试
  function foo(name) {
      this.name = name;
  }
  var obj = {};
  var bar = foo.myBind(obj);
  bar('Jack');
  console.log(obj.name);  // Jack
  var alice = new bar('Alice');
  console.log(obj.name);  // Jack
  console.log(alice.name);    // Alice

3.js实现call?

function  Person (data) {
    console.log(data, 'person')
}
function children(data) {
    console.log(data,'children')
}
Function.prototype.myCall = function(context, ...args){
      if(typeof this !== 'function'){
          throw new TypeError(`${this} is not a function`);
      }
      // 如果没有传或传的值为空对象 context指向window
      context = context || window;     
      context.fn = this;
      const result = context.fn(args.join());
      delete context.fn; //在使用完之后，删除这个方法
      return result; //如果有返回值，将其进行返回
} 
Person.myCall(children,77777,8888) //7777,8888

4.js实现apply?

function  Person (data) {
    console.log(data, 'person')
}
function children(data) {
    console.log(data,'children')
}
Function.prototype.myApply = function(context, args){
      if(typeof this !== 'function'){
          throw new TypeError(`${this} is not a function`);
      }
      if(!Array.isArray(args)){
          throw new TypeError(`${args} is not a Array`);
      }
      context = context || window;
      context.fn = this;
      const result = context.fn(args);
      delete context.fn;
      return result;
} 
Person.myApply(children,[77777,8888])