Why should not declare const variable in export default line in JavaScript ES6?

Question

I have declared const variable like,

"student.js"
 export default const mark= 20;

I am Calling this constant in index.js file

"index.js"
import {mark} from './student';
console.log("Mark Value ::::" + mark);

am getting error????

Answer 1

export default expects an expression. While const is a statement.

You can't do export default const mark = 20 for the same reason you can't do console.log(const mark = 20).

If mark isn't used anywhere else in this file, it should be:

export default 20;

Otherwise it should be:

const mark = 20;
export default mark;

And imported like:

import mark from './student';

Answer 2

Adding to @estus answer, for your code to work change as follows.

"student.js"

export const mark = 20;

"index.js"

import {mark} from './student';
console.log("Mark Value ::::" + mark);

Answer 3

What happens on export default var a = 10, b = 20, c = 30?

Check out this discussion.