Node.js 出口返回未定义

Question

I have the following module:

exports.CONSTANT = "aaaa";

function a() { ... }

module.exports = { a };

For some reasons, when I import like this:

const { CONSTANT, a } = require("./myModule");

the method "a" is defined, but the constant "CONSTANT" is undefined .

Why is this happening?

Answer 1

module.exports overrides the first export and gets returned from the require() call at the end. If you put some logs:

exports.CONSTANT = "aaaa";

function a() {}

console.log(module.exports); // {CONSTANT: "aaaa"}

module.exports = { a };

console.log(module.exports); // {a: ƒ a()}

Try this:

const CONSTANT = "aaaa";

function a() {}

module.exports = { CONSTANT, a };

Or this:

export const CONSTANT = "aaaa";

export function a() {}

Answer 2

You are reassigning the value of module.exports. To fix this, you can do the following:

function a() { ... }

module.exports = {
    CONSTANT: "aaaaa",
    a: a
}

// OR

module.exports.CONSTANT = "aaaaa";

function a() { ... }

module.exports.a = a;

Answer 3

Unfortunately, it is not possible to fit multiple variables in this way { CONSTANT, a} , so I recommend that you fit multiple variables in this way:

{ 
     var1,
     var2,
}

For example:

const { 
     CONSTANT, 
     a
} = require("./Module");