typescript是否允许接口和字符串联合类型？

Question

I'm trying to implement a method like that takes a key argument that is either a string or an instance of the indexable type interface IValidationContextIndex . The implementation looks like this:

  /**
   * Gets all ValidationContext container values.
   * @returns An array of ValidationContext instances contained in the cache.
   */
  public static getValidationContextValues(key: IValidationContextIndex | string ): Array<ValidationContext> {
    if (key instanceof IValidationContextIndex ) [
      return Object.values(<any> key);
    ]
    else {
      const vci = ValidationContainer.cache[<string>key];
      return Object.values(<any> vci);
    }
  }  

Typescript give the following error for the if block:

[ts] 'IValidationContextIndex' only refers to a type, but is being used as a value here.

Any ideas on how to fix this?

For most interface I think it's possible to add a type property ( type: 'IValidationContextsIndex' ; ), but that does not work in this case since the the interface is an indexable type interface ....

Answer 1

有一种方法可以在运行时检查typescript中的类型，因为几乎所有内容都会在转换后成为一个对象，所以你可能需要做一些定义为用户定义的类型保护的东西

Answer 2

I think this will do it (Per the tip from @indrakumara):

    /**
     * Gets all ValidationContext container values fpr a 
     * Object_property string valued key or a key that is an instance of 
     * IValidationContextIndex).
     * @returns An array of ValidationContext instances contained in the cache that corresponds to a specific Object_property key.
     */
    public static getValidationContextValues(key: any ): Array<ValidationContext> {
      if (typeof key === `string` ) {
        const vci = ValidationContainer.cache[<string>key];
        return Object.values(<any> vci);
      }
      else {
        return Object.values(<IValidationContextIndex> key);
      }
    }  

Answer 3

Interfaces in typescript doesn't transpile into any code in javascript. So in your code, "instanceof IValidationContextIndex", IValidationContextIndex doesn't exist in javascript.

Change your interface to class or have a class implementing the interface and then check if passed parameter is instanceof that class.