given this code:

给定此代码：

/**
 * Create a stream from an array of car objects.
 */
from([
  { name: 'Porsche', model: '911' },
  { name: 'Porsche', model: '911' },
  { name: 'Ferrari', model: 'F40' }
]).pipe(
  /**
   * Use keySelectorFn to return car names for use in comparison
   */
  distinctUntilChanged(null, (car) => car.name)
)
.subscribe(console.log);

// console output: 
// {name: "Porsche", model: "911"}
// {name: "Ferrari", model: "F40"}

TS complains that Argument of type 'null' is not assignable to parameter of type '(previous: unknown, current: unknown) => boolean'.

TS报告类型为‘Null’的参数不能赋值给类型为‘(Previor：Uncern，Current：Uncern)=>Boolean’的参数。

If I change it to undefined, the same error.

如果我将其更改为未定义，则会出现相同的错误。

Even in the rxjs docs is undefined used:

即使在rxjs文档中也未定义使用：

// A stream of updates to a given account
const accountUpdates$ = of(
  { updatedBy: 'blesh', data: [] },
  { updatedBy: 'blesh', data: [] },
  { updatedBy: 'ncjamieson', data: [] },
  { updatedBy: 'ncjamieson', data: [] },
  { updatedBy: 'blesh', data: [] }
);
 
// We only want the events where it changed hands
const changedHands$ = accountUpdates$.pipe(
  distinctUntilChanged(undefined, update => update.updatedBy)
);

In this code example I also get the same error.

在此代码示例中，我也收到了相同的错误。

So, the question is: how to set the comparer function to null/undefined without error?

因此，问题是：如何将比较器函数设置为空/未定义而不出错？

My TS version is 4.9.3. RxJs version is 7.5.0.

我的TS版本是4.9.3。RxJs版本为7.5.0。

This looks like it may be a quirk in the typing for distinctUntilChanged. The error would probably go away if you disabled strictNullChecks in your tsconfig.json file.

这看起来可能是differtUntilChanged的输入过程中的一个怪癖。如果您在tsfig.json文件中禁用了strictNullChecks，该错误可能会消失。

However, you can just use distinctUntilKeyChanged instead:

但是，您可以只使用DistertUntilKeyChanged：

distinctUntilKeyChanged('name');

distinctUntilChanged((prev:any,curr:any) => prev.name === curr.name)