Ngrx Store实现源代码的MemoizedSelector学习笔记

2021-12-13 00:04:51

定义一个类型AnyFn，代表任意的函数：

  export type AnyFn = (...args: any[]) => any; 

  let a: AnyFn;

  a = (data) => console.log(data);

  a('Jerry');

  a = 1; // 语法错误

上面代码将1赋给a，会引起编译错误，因为1的类型是number.

定义一个MemoizedProjection类型：

export type MemoizedProjection = {
    memoized: AnyFn;
    reset: () => void;
    setResult: (result?: any) => void;
    clearResult: () => void;
};

定义一个变量，类型为MemoizedProjection：


let a: MemoizedProjection;

let b = (data) => console.log(data);

a.memoized = b;
a.reset = () => console.log('reset');
a.setResult = (result) => console.log(result);
a.clearResult = () => console.log('clear');

上述代码执行会报错误：

Uncaught TypeError: Cannot set property ‘memoized’ of undefined: