ES6导出名称与默认导出的差异

Question

在第一种情况下，我使用export，它的行为正如我所期望的

App.js

import * as a from "./a.js";
console.log("a：", a.a); // it would print out "a： a1 "

a.js

let a = "a0";
export { a };
a = "a1";

在第二种情况下，我使用export default，它的行为不像我期望的那样

App.js

import a from "./a.js";
console.log("a：", a); // it would print out "a： a0" ★★★

a.js

let a = "a0";
export default a;
a = "a1";

为什么会发生这种情况?

Answer 1

我不是100%确定这一点，但我的猜测是默认的export在导出时作为模块内的一个单独变量被分配，而命名的export在导入时被评估。

let a = "a0";
// default export assigned to a separate variable. doesn't change if a is reassigned.
const defaultExport = a;
const b = { a };
a = "a1";
// import * as c gets the new value
const c = { a };
// defaultExport hasn't changed
console.log(defaultExport); // a0
// b has the original value
console.log(b); // a0
// c has the new value
console.log(c); // a1