手写promiseA+规范

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function Promise(executor) {
    let self = this;
    self.status = "pending";
    self.value = undefined;
    self.onResolvedCallbacks = [];
    self.onRejectedCallbacks = [];
    function resolve(value) {
      if (value instanceof Promise) {
        return value.then(resolve, reject)
      }
      setTimeout(function () {
        if (self.status == 'pending') {
          self.value = value;
          self.status = 'resolved';
          self.onResolvedCallbacks.forEach(item => item(value));
        }
      });
  
    }
  
    function reject(value) {
      setTimeout(function () {
        if (self.status == 'pending') {
          self.value = value;
          self.status = 'rejected';
          self.onRejectedCallbacks.forEach(item => item(value));
        }
      });
    }
  
    try {
      executor(resolve, reject);
    } catch (e) {
      reject(e);
    }
  }
  function resolvePromise(promise2, x, resolve, reject) {
    if (promise2 === x) {
      return reject(new TypeError('循环引用'));
    }
    let then, called;
  
    if (x != null && ((typeof x == 'object' || typeof x == 'function'))) {
      try {
        then = x.then;
        if (typeof then == 'function') {
          then.call(x, function (y) {
            if (called)return;
            called = true;
            resolvePromise(promise2, y, resolve, reject);
          }, function (r) {
            if (called)return;
            called = true;
            reject(r);
          });
        } else {
          resolve(x);
        }
      } catch (e) {
        if (called)return;
        called = true;
        reject(e);
      }
    } else {
      resolve(x);
    }
  }
  Promise.prototype.then = function (onFulfilled, onRejected) {
    let self = this;
    onFulfilled = typeof onFulfilled == 'function' ? onFulfilled : function (value) {
      return value
    };
    onRejected = typeof onRejected == 'function' ? onRejected : function (value) {
      throw value
    };
    let promise2;
    if (self.status == 'resolved') {
      promise2 = new Promise(function (resolve, reject) {
        setTimeout(function () {
          try {
            let x = onFulfilled(self.value);
            resolvePromise(promise2, x, resolve, reject);
          } catch (e) {
            reject(e);
          }
        });
  
      });
    }
    if (self.status == 'rejected') {
      promise2 = new Promise(function (resolve, reject) {
        setTimeout(function () {
          try {
            let x = onRejected(self.value);
            resolvePromise(promise2, x, resolve, reject);
          } catch (e) {
            reject(e);
          }
        });
      });
    }
    if (self.status == 'pending') {
      promise2 = new Promise(function (resolve, reject) {
        self.onResolvedCallbacks.push(function (value) {
          try {
            let x = onFulfilled(value);
            resolvePromise(promise2, x, resolve, reject);
          } catch (e) {
            reject(e);
          }
        });
        self.onRejectedCallbacks.push(function (value) {
          try {
            let x = onRejected(value);
            resolvePromise(promise2, x, resolve, reject);
          } catch (e) {
            reject(e);
          }
        });
      });
    }
    return promise2;
  }
  Promise.prototype.catch = function (onRejected) {
    return this.then(null, onRejected);
  }
  Promise.all = function (promises) {
    return new Promise(function (resolve, reject) {
      let result = [];
      let count = 0;
      for (let i = 0; i < promises.length; i++) {
        promises[i].then(function (data) {
          result[i] = data;
          if (++count == promises.length) {
            resolve(result);
          }
        }, function (err) {
          reject(err);
        });
      }
    });
  }
  
  Promise.deferred = Promise.defer = function () {
    var defer = {};
    defer.promise = new Promise(function (resolve, reject) {
      defer.resolve = resolve;
      defer.reject = reject;
    })
    return defer;
  }

    module.exports = Promise

可以跑通 npm 包 promises-aplus-tests 的测试用例,npm install promises-aplus-tests -g 跑测试 promises-aplus-tests 文件名

未完待续。。。