在没有异步/等待的异步函数中使用承诺？

Question

我有一个异步/等待功能。我应该如何重写它以保持异步但不使用异步/等待？我想使用promises，但是当我想重写这段代码时，它不起作用......：/

    fruit = 'apple';
    data: any = {};
      constructor(private http: HttpClient, private storage: Storage) {
      }
    
      async function(ex: string): Promise<{}> {
        ex = ex ? ex : await this.storage.get('ex');
        return new Promise<{}>((resolve) => {
          const path = `./exam/${ex || 'apple'}.json`;
          this.fruit = ex;
          this.storage.set('ex', this.fruit );
          this.http.get<{}>(path).subscribe(
            transition => {
              this.data = Object.assign({}, transition || {});
              return resolve(this.data);
            },
            () => {
              this.data = {};
              return resolve(this.data);
            }
          );
        });
      }
    
      get(): string {
        return this.fruit;
      }
    }

Answer 1

async/await 是 Promise 之上的语法糖，提供了一种以同步方式处理异步任务的方法。如果可行，您可以尝试一下：

async function(ex: string): Promise<{}> {
  ex = ex ? ex : await this.storage.get('ex');
    const path = `./exam/${ex || 'apple'}.json`;
    this.fruit = ex;
    this.storage.set('ex', this.fruit );
    try {
      const result = await this.http.get<{}>(path).toPromise();
      this.data = Object.assign({}, result || {});
      return this.data
    } catch (error) {
       console.log(`An error occured ${error}`);
    }
  
}

注意：使用 async/await 或 then/catch 总是好的。