为什么要用角度的方法从“ some.component.ts”中使用“ import {SomeComponent}”，而不是从“ some.component.ts”中使用“ import SomeComponent”？

Question

I write React/Vue. As usual, I like to export/import a default component.

// export
export default class SomeComponent from Component {
    // blahblah
}

// import
import SomeComponent from './some.js'

But when I use angular2+, I found a strange thing. It uses destructive import/export form.

// export
@Component({/* ... */})
export class SomeComponent {
    // blahblah
}

// import
import {SomeComponent} from './some.component.ts'

Why? I think it a little troublesome. It's defined by Typescript rules or contributor?

Answer 1

如果您在class前添加default ，那么您将能够以与React / Vue中相同的方式导入。

Answer 2

A typescript or javascript file can export multiple class( or functions, constants). Due to this behaviour you export your class( or functions, constants) in this fashion:

export class MyClass{}

and import in this fashion:

// import
import {MyClass} from './myClass.ts'

If you are sure that you will export only single class( or functions, constants) then just use following syntax:

//export
export default class MyClass{}
//import
import MyClass from "./myclass.ts"

Answer 3

This is the standard behavior.

It allows you to export several things out of your file.

For instance

export class MyClass {}
export const MyClassMockedForTesting = {};

But if you want to change that, you can use the default keyword like so

export default class MyClass {}

It will export your class and you won't need brackets anymore.

Answer 4

Angular Doesn't use default imports on its packages because default imports are not good. Other people have covered why in seperate posts so i'll link to one here. https://blog.neufund.org/why-we-have-banned-default-exports-and-you-should-do-the-same-d51fdc2cf2ad

Answer 5

如果您使用“从某组件导入某些组件”，除非在某组件中只有一个出口组件，则如果有多个出口组件，则必须使用{}指定要导入的组件