为什么RxJS subscription允许省略arrow函数和以下方法参数? [英] Why does RxJS subscribe allow omitting the arrow function and the following method argument?

问题描述

最近我需要使用RxJS.我试图设计一个错误处理流程，但发现一些奇怪的语法传递方法参数:

Recently I needed to use RxJS. I tried to design an error handling flow, but I discovered some weird syntax passing method arguments:

.subscribe(
    x => {
    },
    console.warn // <- Why does this compile, and warn 'is not 7' in debug console?
);

链接到最小复制:

https://stackblitz.com/edit/rxjs-6-5-error-handle-no-arrow-issue

1. 使用RxJS 6.5
2. 创建一个可观察到的函数
3. 订阅可观察
4. 将参数传递给订阅
5. 只使用,console.warn，不像,error => { console.warn(error); }

1. Use RxJS 6.5
2. Create a function return observable
3. Subscribe to observable
4. Pass parameter into subscribe
5. Just use ,console.warn, not like ,error => { console.warn(error); }

没有箭头功能，它仍然将错误传递给console.warn.为什么?

Without an arrow function, it still passes errors to console.warn. Why?

代码:

import { throwError, concat, of } from "rxjs";
import { map } from "rxjs/operators";

const result = concat(of(7), of(8));

getData(result).subscribe(
  x => {
    console.log("typeof(x)", typeof(x));
    if (typeof(x) === 'string') {
      console.log("x  Error", x);
      return;
    }
    console.log("no error", x);
  },
  console.warn // <- Why does this compile, and warn 'is not 7' in debug console?
);

// pretend service method
function getData(result) {
  return result.pipe(
    map(data => {
      if (data !== 7) {
        throw "is not 7";
      }
      return data;
    })
  );
}

我尝试用Google搜索一些关键字，js，rxjs，angular，省略箭头功能，缺少参数......但我无法找到此处使用的技术.

I tried to google some keywords, js, rxjs, angular, omit arrow function, argument missing,... but I cannot locate what tech is used here.

任何人都可以提供指向该机制的解释链接吗?

以下两个问题是相关的，但没有解释行为，仅说等效":

The following two questions are related but do not explain the behavior, just say "equivalent":

行

map(this.extractTreeData)

map(this.extractTreeData)

等同于

map(tree => this.extractTreeData(tree))

map(tree => this.extractTreeData(tree))

如何将额外的参数传递给RxJS地图运算符

为什么链映射操作符中缺少参数

推荐答案

在JS中

In JS functions are first class objects. When you have the code console.warn no brackets you have a reference to this object but you're not invoking that object, that would require braces console.warn(). For example you can do:

let x = console.warn;
console.log('not happened yet');
x('test');

因此，您的代码很容易以与传递任何其他函数(例如

So your code is simple passing the console.warn function to the parameter of the Subscribe failure in exactly the same manner as you might pass any other function, e.g.

Subscribe(() => {}, () => {});

[为什么]显示警告不是7"

另一部分是您抛出错误throw "is not 7";.因此，Subscribe错误调用的签名是:

[why] show Warn 'is not 7'

The other part of this is that your throwing an error throw "is not 7";. The signature of the error call of Subscribe is thus:

subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void): Subscription;

因此，error的参数的类型为any.因此，throw将Error传递给错误函数处理程序.设置为console.warn，其签名为:

So the parameter of error is of type any. So the throw passes an Error to the error function handler. This is set as console.warn which has a signature of :

console.warn(obj1 [, obj2, ..., objN]);

console.warn本质上将传递给它的任何参数转换为字符串，JS不是强类型化的，这本质上可以归结为

console.warn essentially turns whatever parameter it's passed into a string, JS is not strongly typed and this is essentially down to type coercion, and logs it. the string of throw "is not 7"; is is not 7. So it logs is not 7.

总而言之，我想说的都是有点晦涩难懂，而且可能很难遵循.从技术上讲，这里没有什么错，但是我想说，做以下事情更有意义:

All in all I'd say this is all all a bit cryptic and potentially difficult to follow. There is nothing technically wrong here, but I would say it would make more sense to do the following:

.subscribe(
    x => {
    },
    x => {console.warn(x);} 
);

基于>任何傻瓜都可以编写计算机可以理解的代码的原则.好的程序员编写人类可以理解的代码."

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