如何在switch语句中使用instanceof

本文介绍了如何在switch语句中使用instanceof的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我使用自定义错误（ es6-error ），允许我处理基于他们的课程就像这样：

I use custom errors (es6-error) allowing me to handle errors based on their class like so:

import { DatabaseEntryNotFoundError, NotAllowedError } from 'customError'; function fooRoute(req, res) { doSomethingAsync() .then(() => { // on resolve / success return res.send(200); }) .catch((error) => { // on reject / failure if (error instanceof DatabaseEntryNotFoundError) { return res.send(404); } else if (error instanceof NotAllowedError) { return res.send(400); } log('Failed to do something async with an unspecified error: ', error); return res.send(500); }; }

现在我宁愿为这种类型的流程使用一个开关，导致如下：

Now I'd rather use a switch for this type of flow, resulting in something like:

import { DatabaseEntryNotFoundError, NotAllowedError } from 'customError'; function fooRoute(req, res) { doSomethingAsync() .then(() => { // on resolve / success return res.send(200); }) .catch((error) => { // on reject / failure switch (error instanceof) { case NotAllowedError: return res.send(400); case DatabaseEntryNotFoundError: return res.send(404); default: log('Failed to do something async with an unspecified error: ', error); return res.send(500); } }); }

instanceof 不起作用。所以后者失败。

instanceof doesn't work like that however. So the latter fails.

有没有办法在switch语句中检查其类的实例？

Is there any way to check an instance for its class in a switch statement?

推荐答案

一个好的选择是使用构造函数 属性对象：

A good option is to use the constructor property of the object:

// on reject / failure switch (error.constructor) { case NotAllowedError: return res.send(400); case DatabaseEntryNotFoundError: return res.send(404); default: log('Failed to do something async with an unspecified error: ', error); return res.send(500); }

请注意，构造函数必须与创建对象的对象完全匹配（假设错误是 NotAllowedError 和 NotAllowedError 是的子类）：

Notice that the constructor must match exactly with the one that object was created (suppose error is an instance of NotAllowedError and NotAllowedError is a subclass of Error):

• error.constructor === NotAllowedError 是 true
• error.constructor ===错误是 false

• error.constructor === NotAllowedError is true
• error.constructor === Error is false

这与 instanceof 有所不同，它也可以匹配超级类：

This makes a difference from instanceof, which can match also the super class:

• 错误实例NotAllowedError 是 true
• error instanceof错误是 true

• error instanceof NotAllowedError is true
• error instanceof Error is true

检查这个有趣的帖子关于构造函数财产。