js 自己实现Promise

迷南。 2022-10-14 12:59 169阅读 0赞

function Promise(exector) {
      var _this = this
      this.status = 'pending'
      this.value = undefined
      this.resolveList = []
      this.rejectList = []
    
      try {
        exector(resolve, reject)
      }catch(e) {
        reject(e)
      }
    
      function resolve(value) {
        if(_this.status === 'pending') {
          _this.status = 'fulfilled'
          _this.value = value
          _this.resolveList.forEach(item=> {
            item(_this.value)
            _this.resolveList.shift()
          })
        }
      }
    
      function reject(value) {
        if(_this.status === 'pending') {
          _this.status = 'rejected'
          _this.value = value
          _this.rejectList.forEach(item=> {
            item(_this.value)
            _this.rejectList.shift()
          })
        }
      }
    }
    
    Promise.prototype.then = function(resolveCallback, rejectCallback) {
      var _this = this
      if(this.status === 'fulfilled') {
        return new Promise((resolve, reject)=> {
          var result = resolveCallback(_this.value)
          if(result instanceof Promise) {
            result.then(resolve, reject)
          }else {
            resolve(result)
          }
        })
      }
    
      if(this.status === 'rejected') {
        return new Promise((resolve, reject)=> {
          var result = rejectCallback(_this.value)
          if(result instanceof Promise) {
            result.then(resolve, reject)
          }else {
            reject(result)
          }
        })
      }
    
      if(this.status === 'pending') {
        return new Promise((resolve, reject)=> {
          _this.resolveList.push(function() {
            var result = resolveCallback(_this.value)
            if(result instanceof Promise) {
              result.then(resolve, reject)
            }else {
              resolve(result)
            }
          })
    
          _this.rejectList.push(function() {
            var result = rejectCallback(_this.value)
            if(result instanceof Promise) {
              result.then(resolve, reject)
            }else {
              reject(result)
            }
    
          })
    
        })
      }
    }
    
    
    new Promise((resolve, reject)=> {
      resolve(666)
    }).then((data)=> {
      console.log('resolve1:' + data)
      return 999
    }).then((data)=> {
      console.log('resolve2:' + data)
    })
    //resolve1: 666
    //resolve2: 999
    
    new Promise((resolve, reject)=> {
      resolve(666)
    }).then((data)=> {
      console.log('resolve1:' + data)
      return new Promise((resolve, reject)=> {
        resolve(999)
      })
    }).then((data)=> {
      console.log('resolve2:' + data)
    })
    //resolve1: 666
    //resolve2: 999

Promise.all = function(iterable) {
      return new Promise((resolve, reject) => {
        let result = []
        for(const item of iterable) {
          item.then(data => {
            result.push(data)
          }, reason=> {
            result = reason
            return
          })
        }
    
        resolve(result)
      })
    }
    
    //下面是测试用例
    let p1 = new Promise((resolve, reject) => {
      resolve(666)
    })
    
    let p2 = new Promise((resolve, reject) => {
      resolve(888)
    })
    
    let p3 = new Promise((resolve, reject) => {
      resolve(999)
    })
    
    let p6 = new Promise((resolve, reject) => {
      reject(222)
    })
    
    let p4 = Promise.all([p1, p2, p3])
    
    p4.then(data => {
      console.log(data)
    })
    //[666, 888, 999]
    let p7 = Promise.all([p1, p3, p6])
    
    p7.then(data => {
      console.log(data)
    })
    //222

Promise.race = function(iterable) {
      return new Promise((resolve, reject) => {
        for(const item of iterable) {
          item.then(data => {
            resolve(data)
          }, reason=> {
            reject(reson)
          })
        }
      })
    }
    //测试用例
    var p1 = new Promise(function(resolve, reject) {
        setTimeout(resolve, 500, 'one');
    });
    
    var p2 = new Promise(function(resolve, reject) {
        setTimeout(resolve, 100, 'two');
    });
    
    Promise.race([p1, p2]).then(function(value) {
      console.log(value);
      // Both resolve, but promise2 is faster
    });
    //two

Promise.resolve = function(data) {
      return new Promise((resolve, reject) => {
        resolve(data)
      })
    }
    
    //测试用例
    var p1 = Promise.resolve(123);
    
    p1.then(function(value) {
      console.log(value);
    });
    //123
    
    Promise.reject = function(data) {
      return new Promise((resolve, reject) => {
        reject(data)
      })
    }