ES6 模块范围

Question

I have the code:

// lib.js
var a = "a";
export var b = "b";

// main.js
console.log(a); // "a" variable is not available in a global scope
import {b} from "lib";
console.log(a); // is "a" variable available in a global scope or only in a module scope?

Can I use "a" variable in a global scope after module importing or is it available only in a module scope? Will ES6 modules have a similar working principle like this trick:

// module    
exports.module1 = (function(){ var a = "a"; })(); // "a" variable is not available in a global scope

Answer 1

Can I use "a" variable in a global scope after module importing or is it available only in a module scope?

It's only available inside the module it was declared in.

Will ES6 modules have a similar working principle like this trick: [...]

Basically yes.

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ES6 has these kinds of scopes, order from "top" to "bottom":

• Global scope
• Module scope
• Function scope
• Block scope

Answer 2

You can do globalThis.a = "a" and access it after that module has loaded. See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis

Answer 3

lets say you are exporting something to another module. example you are exporting var b = 'b' , but you are not exporting the var a = 'a' . this means you are only able to use var a = 'a' in lib.js , It is local to the module it was declared in and only can be used in that module. var a is scoped to the lib.js module.