什么是“出口默认"?在 JavaScript 中? [英] What is "export default" in JavaScript?

问题描述

文件:SafeString.js

// Build out our basic SafeString type
function SafeString(string) {
  this.string = string;
}

SafeString.prototype.toString = function() {
  return "" + this.string;
};

export default SafeString;

我以前从未见过export default.export default 是否有更容易理解的等效内容?

I have never seen export default before. Are there any equivalent stuff for export default that can be easier to understand?

推荐答案

它是 ES6 模块系统的一部分，在此处描述.该文档中还有一个有用的示例:

It's part of the ES6 module system, described here. There is a helpful example in that documentation, also:

如果模块定义了默认导出:

If a module defines a default export:

// foo.js
export default function() { console.log("hello!") }

然后您可以通过省略大括号来导入该默认导出:

then you can import that default export by omitting the curly braces:

import foo from "foo";
foo(); // hello!

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更新:截至 2015 年 6 月，模块系统定义在 §15.2 和 export 语法在 §15.2.3.

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Update: As of June 2015, the module system is defined in §15.2 and the export syntax in particular is defined in §15.2.3 of the ECMAScript 2015 specification.

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