未捕获（承诺中）：TypeError：无法读取未定义的属性“userSubject”类型错误：无法读取未定义的属性“userSubject”答案

【问题标题】：Uncaught (in promise): TypeError: Cannot read property 'userSubject' of undefined TypeError: Cannot read property 'userSubject' of undefined未捕获（承诺中）：TypeError：无法读取未定义的属性“userSubject”类型错误：无法读取未定义的属性“userSubject”
【发布时间】：2020-05-03 12:04:35
【问题描述】：

我想打电话

login(username, password) {    
  return Parse.User.logIn(username, password)
    .then(function (user) {
      // store user details and jwt token in local storage to keep user logged in between page refreshes
      localStorage.setItem('user', JSON.stringify(user));
      console.log(user);
      this.userSubject.next(user);
      return user;
    });
}

和这个一样

login(username, password) {
  return this.http.post<user>(`${environment.apiUrl}/users/authenticate`, { username, password })
    .pipe(map(user => {
      // store user details and jwt token in local storage to keep user logged in between page refreshes
      localStorage.setItem('user', JSON.stringify(user));
      console.log(user);
      this.userSubject.next(user);
      return user;
  }));
}

但它会导致错误

Uncaught (in promise): TypeError: Cannot read property 'userSubject' of undefined
TypeError: Cannot read property 'userSubject' of undefined

【问题讨论】：

标签： javascript angular promise rxjs

【解决方案1】：

问题在于您使用的是普通函数而不是箭头函数。一个普通的函数有自己的this指针。

只需使用箭头函数。

login(username, password) {

return Parse.User.logIn(username, password)
  .then((user) => { // <-- here is the change
    localStorage.setItem('user', JSON.stringify(user));
    console.log(user);
    this.userSubject.next(user);
    return user;
  });
}

【讨论】：

非常感谢撒旦兄弟