javascript - 如果从不运行，为什么会这样

Question

我想要实现的是:
- 首先回调运行并且
- this.auth.javaAuthToken，它是另一个文件中的属性，被初始化为 token 的值。
- 之后，调用此函数:return this.auth.getUserFiles();

如果我这样做:

resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<any> {
   let token = null;
    this.auth.emailListCleaningUserDetail().subscribe((res: any)=>{
    token = res.body.data.access_token;
    token = this.auth.javaAuthToken;
     return this.auth.getUserFiles();
  });

然后我收到一个错误:

function must return a value

所以我编写了下面的代码来检查 token 是否存在。如果是这样，那么我调用该函数并返回。

resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<any> {
   let token = null;
    this.auth.UserDetail().subscribe((res: any)=>{
    token = res.body.data.access_token;
    token = this.auth.javaAuthToken;
    console.log(token);
    console.log('inside fun');  
  });
    if(token) {
      console.log('inside if outside fun');
      this.auth.javaAuthToken = token;
      return this.auth.getUserFiles();
    }
    console.log('outside if and fun')
  }
}  

当我运行该程序时，
- 首先打印 outside if and fun，
- 然后打印 token ，并且
- 然后打印inside fun。

Answer 1

很简单，当您尝试访问 token 时(当您返回结果时)，结果尚不可用。在异步函数中，您必须等待该值或订阅该事件。

如果您订阅了该事件，则只能访问订阅内的值。

resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<any> {
   let token = null;
    this.auth.UserDetail().subscribe((res: any)=>{
    token = res.body.data.access_token;
    token = this.auth.javaAuthToken;
    console.log(token);
    console.log('inside fun');  
    
    // This is called when you receive your result which can be later as the code below as this is async

  });

// token is always null because its declared as null before
// when this code runs, there is no result of your Service yet
    if(token) {
      console.log('inside if outside fun');
      this.auth.javaAuthToken = token;
      return this.auth.getUserFiles();
    }
    console.log('this runs right after the code before but the result is not available yet')
  }
}

我想知道这是否也是异步的:

this.auth.getUserFiles();

然后你可以做这样的事情

LoadUserData = async event => {

    var token = null;
    var userfiles = null;
    try {
        var response = await this.auth.UserDetail()
        if (response.data != null) {
            token = response.data.access_token;        
            console.log('Receiving result: '+JSON.stringify(response.data));
        }
    } catch (error) {
        console.log('ERROR: '+error)
    }

    try {
          var responseUserFiles = await this.auth.getUserFiles();
          if (responseUserFiles.data != null) {
              // do something with your userfiles
              userfiles = responseUserFiles.data;
              console.log('Receiving result: '+JSON.stringify(responseUserFiles.data));
          }
      } catch (error) {
          console.log('ERROR: '+error)
    }

    // Here you can return what you want, userfiles  or token
    return userfiles;
}