问个 ts 函数重载的问题？

Question

  private handleParams(method: Method.Add, params: AddParams)
  private handleParams(method: Method.Reduce, params: ReduceParams)
  private handleParams(method: Method, params: AddParams | ReduceParams) {
    switch (method) {
      case Method.Add:
        // 到了这里
        // params 还是 AddParams | ReduceParams 这个类型
        // 预期是 AddParams 类型，应该怎么写呢
        break;
        // ...
    }

Answer 1

1. 我不确定问题描述无效的产生原因；
2. 可以参考如下写法，看是否可以满足你的需求；

enum Method {
  Add = 'Add',
  Reduce = 'Reduce',
}

interface AddParams {
  method: Method.Add;
  name: string;
}

interface ReduceParams {
  method: Method.Reduce;
  length: number;
}

class Aaa {
  private handleParams(params: AddParams): string;
  private handleParams(params: ReduceParams): number;
  private handleParams(params: AddParams | ReduceParams): number | string {
    const method = params.method;

    switch (method) {
      case Method.Add:
        return params.name;
      case Method.Reduce:
        return params.length;
      default:
        return 0;
    }
  }
}