从 '.' 导入 {} 是什么意思做？

Question

I was looking at some source code of a library and I saw this import

import {SheetsRegistry, JssProvider, withStyles} from '.'

What does this do? How does it import from '.'?

Answer 1

The code you shared imports those declarations from index.js in the same directory.

index.js:

// @flow
import withStyles from './withStyles'

export {ThemeProvider, withTheme, createTheming, useTheme} from 'theming'
export {default as createUseStyles} from './createUseStyles'
export {default as JssProvider} from './JssProvider'
export {default as jss} from './jss'
export {SheetsRegistry, createGenerateId} from 'jss'
export {default as JssContext} from './JssContext'
export {default as styled} from './styled'
export {default as jsx, create as createJsx} from './jsx'
export {withStyles}

// Kept for backwards compatibility.
export default withStyles

In this example, index.js is being used to re-export some of the declarations within the src directory. This pattern makes it easier to move the declarations around without having to rewrite many imports.

Answer 2

******The difference between named exports and default exports.******

1-named exports

export function, constant, variable...etc in Constant.js

export const CREATE = 'CREATE';
export const DELETE = 'DELETE';

import like this in index.js

import {CREATE,DELETE} from './Constants';

2-default exports

export it in Constant.js

const update = ()=> 'UPDATE'
export default update();

and import like this in index.js

import UPDATE from './Constants';