模块

export default vs export

• export default 只能出现一次，export not
• export default ,xx 可以是{},function(){},and others
• export ,xx可以是{}, const str = xx等形式

export

* export 字符串
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# demo.js
export default 'hello world'

* export default {}
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#demo.js
export default {
    hello:'hello',
}

* export {}
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const hello = 'hello'
export {
    hello,
}
#or 
export const hello = 'hello'

import

* import 字符串
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# foo = 'hello world'
import foo from demo.js

* import from default 
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# foo =  {
    hello:'hello',
}
import foo from demo.js

* import {}
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# hello = 'hello'
import { hello } from demo.js