[英]Is `export { foo as default }` valid ES2015?
I received an issue on GitHub about my ES2015 module import/export validating plugin for ESLint not recognizing the default
export in the following syntax: 我在GitHub上收到一个关于ESLint的ES2015模块导入/导出验证插件的问题,但没有通过以下语法识别default
导出:
export {
foo as default,
bar
}
where my plugin will lint the following (equivalent?) syntax no problem: 我的插件将lint下面(等效?)语法没问题:
export default foo;
export const bar = ..;
Both Babel and Esprima parse similar syntax without errors, and this works for code using Babel on both ends (import and export). Babel和Esprima都解析了类似的语法而没有错误,这适用于两端使用Babel的代码(导入和导出)。
However, I'm not convinced the spec allows the former export { x as default }
form: 但是,我不相信规范允许前export { x as default }
形式:
For each
IdentifierName
n
inReferencedBindings
ofExportClause
: It is a Syntax Error if StringValue of n is a ReservedWord or if the StringValue of n is one of: "implements", "interface", "let", "package", "private", "protected", "public", "static", or "yield". 对于ExportClause
ReferencedBindings
的每个IdentifierName
n
:如果n的StringValue是ReservedWord,或者n的StringValue是以下之一,则它是语法错误:“implements”,“interface”,“let”,“package”,“private” ,“受保护”,“公共”,“静态”或“收益”。
ReservedWord
does include default
, though I think one could argue that ReferencedBindings
is referring specifically to the module-local identifier names that are being exported (ie foo
) and not the exported name itself. ReservedWord
确实包含default
,但我认为有人可能认为ReferencedBindings
特指的是正在导出 的模块本地标识符名称 (即foo
)而不是导出的名称本身。
It also generally seems like a weird thing to be able to export reserved words; 能够导出保留字通常似乎是一件奇怪的事情; Babel will happily also allow something like 巴别塔也很乐意也允许这样的事情
// ./foo.js
export { foo as yield }
// ./mod.js
import { yield as nonReservedIdentifier } from './foo'
So, in summary: is export { foo as default }
a valid way to export a default in ES2015? 那么,总结一下: export { foo as default }
是在ES2015中导出默认值的有效方法吗?
Yes, ReferencedBindings refers only to the first IdentifierName. 是的, ReferencedBindings仅指第一个IdentifierName。 So 所以
export { default as something } // or
export { default }
is invalid, but 是无效的,但是
export { something as default }
is not. 不是。 ESLint will need a fix here. ESLint需要在这里修复。
Yes, it's valid. 是的,它是有效的。 I'll break it down. 我会把它分解。
: :
export { foo as default }
This matches the following productions (from least to most specific): 这符合以下制作(从最少到最具体):
export ExportClause ExportClause : { ExportsList } ExportsList : ExportSpecifier ExportSpecifier : IdentifierName as IdentifierName
Then you have the early error semantics : 然后你有早期的错误语义 :
15.2.3.1 Static Semantics: Early Errors 15.2.3.1静态语义:早期错误
ExportDeclaration : export ExportClause ;
For each
IdentifierName
n
inReferencedBindings
ofExportClause
: It is a Syntax Error ifStringValue
ofn
is aReservedWord
... 对于ExportClause
ReferencedBindings
的每个IdentifierName
n
:如果n
StringValue
是ReservedWord
,则为语法错误...
These apply to any productions matching export ExportClause
, including your example syntax. 这些适用于与export ExportClause
匹配的任何产品,包括您的示例语法。 This invokes the ReferencedBindings
algorithm. 这将调用ReferencedBindings
算法。
The ReferencedBindings
algorithm that applies to that most specific production matched by this syntax is: 适用于与此语法匹配的最特定生产的ReferencedBindings
算法是:
ExportSpecifier : IdentifierName as IdentifierName
Return a
List
containing the firstIdentifierName
. 返回包含第一个IdentifierName
的List
。
So you see that the restriction regarding ReservedWord
and the other listed values is only applied to the foo
part of the syntax in your example. 因此,您会看到有关ReservedWord
和其他列出值的限制仅适用于示例中语法的foo
部分。
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