`export {foo as default}`有效的ES2015？ [英] Is `export { foo as default }` valid ES2015?

问题描述

我在GitHub上收到了关于ESL15的ES2015模块导入/导出验证插件的问题不能以下列语法识别 default export：

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:

export { 
    foo as default,
    bar
}

我的插件将lint以下（等效？）语法没有问题：

where my plugin will lint the following (equivalent?) syntax no problem:

export default foo;
export const bar = ..;

Babel 和 Esprima 解析类似的语法，没有错误，这适用于使用Babel两端的代码（导入和导出）。

Both Babel and Esprima parse similar syntax without errors, and this works for code using Babel on both ends (import and export).

然而，我不相信 spec 允许以前的导出{x作为默认} 形式：

However, I'm not convinced the spec allows the former export { x as default } form:

对于中的每个标识符名称 n ReferencedBindings ExportClause ：如果n的StringValue为ReservedWord，或者如果n的值为implements，则为语法错误， interface，let，package，private，protected，public，static或yield。

For each IdentifierName n in ReferencedBindings of ExportClause : 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".

ReservedWord 确实包括 default ，虽然我认为可以认为 ReferencedBindings 是指具体涉及导出的模块 - 本地标识符名称 （即 foo ），而不是导出的名称本身。

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 (i.e. foo) and not the exported name itself.

通常似乎还有一个奇怪的事情可以导出保留字Babel也会很高兴地允许像

It also generally seems like a weird thing to be able to export reserved words; Babel will happily also allow something like

// ./foo.js
export { foo as yield }
// ./mod.js
import { yield as nonReservedIdentifier } from './foo'

所以，总结：是 export {foo as default} 一种在ES2015中导出默认值的有效方法？

So, in summary: is export { foo as default } a valid way to export a default in ES2015?

推荐答案

是的， 引用绑定 仅引用第一个IdentifierName。所以

Yes, ReferencedBindings refers only to the first IdentifierName. So

export { default as something } // or
export { default }

无效，但

export { something as default }

不是。 ESLint需要在这里修复。

is not. ESLint will need a fix here.

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