如何将Promise<any[]>转换为any[]？async/await与Promise类型错误问题

错误提示 #

Type 'Promise<any[]>' is missing the following properties from type 'any[]': length, pop, push, concat, and 29 more.
错误出现在语句：
objectList = this.markRequired(objectList, requiredList, typeCodeName);

相关代码 #

async applyRequiredTypes(objectList: any[], typeCodeName: any, requiredList: any[]) {
  objectList = objectList || [];
  requiredList = requiredList || [];
  objectList = this.markRequired(objectList, requiredList, typeCodeName);
  ...
}

async markRequired(itemList: any[], requiredList: any[], typeCodeName: any) {
  return itemList.map((item: any) => {
    item.required = requiredList.some((requiredTypeCode) => {
      return requiredTypeCode === item[typeCodeName];
    });
    return item;
  });
}

原因 #

你给markRequired加了async关键字，不管函数内部有没有异步操作，只要加了async，函数就会自动返回一个Promise对象，而不是你写的map返回的数组。但objectList的类型是any[]，把Promise赋值给数组类型的变量，类型不匹配，所以TS报错。

解决办法 #

方法一：移除不必要的async #

因为这个函数里全是同步操作（map和some都是同步方法），完全不需要async修饰。去掉后函数直接返回数组，类型就匹配了：

markRequired(itemList: any[], requiredList: any[], typeCodeName: any) {
  return itemList.map((item: any) => {
    item.required = requiredList.some((requiredTypeCode) => {
      return requiredTypeCode === item[typeCodeName];
    });
    return item;
  });
}

方法二：如果需要保留async（比如后续要加异步逻辑） #

就在调用markRequired的时候用await解析Promise的结果，因为applyRequiredTypes本身已经是async函数，这么做是合法的：

async applyRequiredTypes(objectList: any[], typeCodeName: any, requiredList: any[]) {
  objectList = objectList || [];
  requiredList = requiredList || [];
  // 用await获取Promise内部的数组结果
  objectList = await this.markRequired(objectList, requiredList, typeCodeName);
  ...
}

内容的提问来源于stack exchange，提问作者pillar star