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Is there any advantage to default export compared to named export? [duplicate]

I have referred all the questions in stackoverflow.
But none of the suggested why and when to use default export.
I just saw that default can be metioned "When there is only one export in a file"
Any other reason for using default export in es6 modules?

Some differences that might make you choose one over the other:
Named Exports
Can export multiple values
MUST use the exported name when importing
Default Exports
Export a single value
Can use any name when importing
This article does a nice job of explaining when it would be a good idea to use one over the other.

It's somewhat a matter of opinion, but there are some objective aspects to it:
You can have only one default export in a module, whereas you can have as many named exports as you like.
If you provide a default export, the programmer using it has to come up with a name for it. This can lead to inconsistency in a codebase, where Mary does
import example from "./example";
...but Joe does
import ex from "./example";
In contrast, with a named export, the programmer doesn't have to think about what to call it unless there's a conflict with another identifier in their module.¹ It's just
import { example } from "./example";
With a named export, the person importing it has to specify the name of what they're importing. They get a nice early error if they try to import something that doesn't exist.
If you consistently only use named exports, programmers importing from modules in the project don't have to think about whether what they want is the default or a named export.
¹ If there is a conflict (for instance, you want example from two different modules), you can use as to rename:
import { example as widgetExample } from "./widget/example";
import { example as gadgetExample } from "./gadget/example";

You should almost always favour named exports, default exports have many downsides
Problems with default exports:
Difficult to refactor or ensure consistency since they can be named anything in the codebase other than what its actually called
Difficult to analyze by automated tools or provide code intellisense and autocompletion
They break tree shaking as instead of importing the single function you want to use you're forcing webpack to import the entire file with whatever other dead code it has leading to bigger bundle sizes
You can't export more than a single export per file
You lose faster/direct access to imports
checkout these articles for a more detailed explanation:
https://blog.neufund.org/why-we-have-banned-default-exports-and-you-should-do-the-same-d51fdc2cf2ad
https://humanwhocodes.com/blog/2019/01/stop-using-default-exports-javascript-module/
https://rajeshnaroth.medium.com/avoid-es6-default-exports-a24142978a7a

With named exports, one can have multiple named exports per file. Then import the specific exports they want surrounded in braces. The name of imported module has to be the same as the name of the exported module.
// imports
// ex. importing a single named export
import { MyComponent } from "./MyComponent";
// ex. importing multiple named exports
import { MyComponent, MyComponent2 } from "./MyComponent";
// ex. giving a named import a different name by using "as":
import { MyComponent2 as MyNewComponent } from "./MyComponent";
// exports from ./MyComponent.js file
export const MyComponent = () => {}
export const MyComponent2 = () => {}
You can also alias named imports, assign a new name to a named export as you import it, allowing you to resolve naming collisions, or give the export a more informative name.
import MyComponent as MainComponent from "./MyComponent";
You can also Import all the named exports onto an object:
import * as MainComponents from "./MyComponent";
// use MainComponents.MyComponent and MainComponents.MyComponent2 here
One can have only one default export per file. When we import we have to specify a name and import like:
// import
import MyDefaultComponent from "./MyDefaultExport";
// export
const MyComponent = () => {}
export default MyComponent;
The naming of import is completely independent in default export and we can use any name we like.
From MDN:
Named exports are useful to export several values. During the import, one will be able to use the same name to refer to the corresponding value.
Concerning the default export, there is only a single default export per module. A default export can be a function, a class, an object or anything else. This value is to be considered as the “main” exported value since it will be the simplest to import.

There aren't any definitive rules, but there are some conventions that people use to make it easier to structure or share code.
When there is only one export in the entire file, there is no reason to make it named.
Also, when your module has one main purpose, it could make sense to make that your default export. In those cases you can extra named exports
In react for example, React is the default export, since that is often the only part that you need. You don't always Component, so that's a named export that you can import when needed.
import React, {Component} from 'react';
In the other cases where one module has multiple equal (or mostly equal) exports, it's better to use named exports
import { blue, red, green } from 'colors';

1st Method:-
export foo; //so that this can be used in other file
import {foo} from 'abc'; //importing data/fun from module
2nd Method:-
export default foo; //used in one file
import foo from 'blah'; //importing data/fun from module
3rd Method:-
export = foo;
import * as foo from 'blah';
The above methods roughly compile to the following syntax below:-
//all export methods
exports.foo = foo; //1st method
exports['default'] = foo; //2nd method
module.exports = foo; //3rd method
//all import methods
var foo = require('abc').foo; //1st method
var foo = require('abc')['default']; //2nd method
var foo = require('abc'); //3rd method
For more information, visit to Default keyword explaination
Note:- There can be only one export default in one file.
So whenever we are exporting only 1 function, then it's better to use default keyword while exporting

EASIEST DEFINITION TO CLEAR CONFUSIONS
Let us understand the export methods, first, so that we can analyze ourselves when to use what, or why do we do what we do.
Named exports: One or more exports per module. When there are more than one exports in a module, each named export must be restructured while importing. Since there could be either export in the same module and the compiler will not know which one is required unless we mention it.
//Named export , exporting:
export const xyz = () =>{
}
// while importing this
import {xyx} from 'path'
or
const {xyz} = require(path)
The braces are just restructuring the export object.
On the other hand , default exports are only one export per module , so they are pretty plain.
//exporting default
const xyz =() >{
};
export default xyz
//Importing
import xyz from 'path'
or
const xyz = require(path)
I hope this was pretty simple to understand, and by now you can understand why you import React modules within braces...

Named Export: (export)
With named exports, one can have multiple named exports per file. Then import the specific exports they want surrounded in braces. The name of imported module has to be the same as the name of the exported module.
// imports
// ex. importing a single named export
import { MyComponent } from "./MyComponent";
// ex. importing multiple named exports
import { MyComponent, MyComponent2 } from "./MyComponent";
// ex. giving a named import a different name by using "as":
import { MyComponent2 as MyNewComponent } from "./MyComponent";
// exports from ./MyComponent.js file
export const MyComponent = () => {}
export const MyComponent2 = () => {}
Import all the named exports onto an object:
// use MainComponents.MyComponent and MainComponents.MyComponent2 here
import * as MainComponents from "./MyComponent";
Default Export: (export default)
One can have only one default export per file. When we import we have to specify a name and import like:
// import
import MyDefaultComponent from "./MyDefaultExport";
// export
const MyComponent = () => {}
export default MyComponent;
Note: The naming of import is completely independent in default export and we can use any name we like.
Here's a great answer that explains default and named imports in ES6

Having problem with import in ES6 module: property is not exported

I'm currently working with redux, and I'm exporting an object with the type properties to my reducer file.
My types.js file:
const Types = {LOG_IN:'LOG_IN',REGISTER:'REGISTER'};
export default Types;
My reducer.js file:
import {LOG_IN,REGISTER} from './types';
//CODE HERE
When I compile, however, CRA give me an error:
Attempted import error: 'LOG_IN' is not exported from './types'.
Curiously enough, this code works:
import Types from './types';
const {LOG_IN,REGISTER} = Types;
Why is it that my code structure doesn't work with that form of importing while React's and Redux's code does? Thank you in advance.

You need to explicitly define a named export for each constant for that to work.
export const LOG_IN = 'LOG_IN';
export const REGISTER = 'REGISTER';
Importing a named export is not the same thing as destructuring a default export, which is what's happening when you do this:
import Types from './types';
const {LOG_IN,REGISTER} = Types;
You can read more on this here. Other code you find in the wild might appear to work like you describe because it's actually defining its exports like this:
module.exports = {
LOG_IN: 'LOG_IN'
}

I think is because you export Types, if tou can use LOG_IN for example you need to access Types.LOG_IN, and the code const {LOG_IN,REGISTER} = Types; works because you are using destructuring
the
import Types from './types';
are correct
an then try to access with Types.REGISTER

Exporting multiple constants as one json

I am having few constant files and an index.js file in a constant folder.
index.js file,
import * as env from "./env.constants";
import * as httpC from "./http.constants";
import * as localStorage from "./localStorage.constants";
import * as routes from "./routes.constants";
const appConstants = {
...env,
...httpC,
...localStorage,
...routes
};
console.log(appConstants);
export default appConstants;
and my constant files are as follows ,
http.constants.js
export const GET = "GET";
export const POST = "POST";
Other files are having same exports with different names.
The console output of index.js is a json, containing all the constants.
But when I am importing them as
import * as test from "./constants";
console.log(test);
I am getting the following output in my browser,
I want to use the constants in a single import,
import { GET, LOGIN_URL } from 'constants';
What have I missed ?

But when I am importing them as
import * as test from "./constants";
console.log(test);
I am getting the following output in my browser,
That's because you're importing the module's module namespace object (that's what import * does), and then outputting it directly.
To get the constants file you want, don't do the import * as and then combine them into an object and export that object as a default;instead, simply re-export them like this:
export * from "./env.constants";
export * from "./http.constants";
export * from "./localStorage.constants";
export * from "./routes.constants";
That will export all the named exports from all of those modules as named exports from the constants module.
What you were trying to do is a relatively common misunderstanding of the JavaScript module system, as compared to the CommonJS-like module system of Node.js. Named exports are not just properties on an object that's the default export. Named exports are their own first-level thing. If you do:
export default {
foo: 42
};
...you can't do import { foo } from "./mod" to import it, because foo isn't a named export, it's just a property on the default export, which is an object.
I am having few constant files and an index.js file in a constant folder.
...
import { GET, LOGIN_URL } from 'constants';
FWIW, relying on that to import a index.js file from the constants folder is relying on Node.js-specific features, not anything built into the JavaScript module system. If you only expect it to work in Node.js, that's fine, but just beware that it's not standard.

Using Import * from single export

I am not used to seeing a import * often
The react + readux code I am going through uses import *
According to firefox documentation about import *
This inserts myModule into the current scope, containing all the
exports from the module in the file located in /modules/my-module.js.
suppose we have an export statement like this in our code (call it articleTypes.js) .
export const ARTICLES_FETCHED = 'articles.ARTICLES_FETCHED';
Doing this, Would make actually probably make sense we didn't use export default above
import * as types from './actionTypes'
But If we alter the above lines like this
export default const ARTICLES_FETCHED = 'articles.ARTICLES_FETCHED';
and do something like this
import types from './actionTypes'
Will it work the same way as the above code? or will this actually work? and will this be a better approach?

But If we alter the above lines like this
export default const ARTICLES_FETCHED = 'articles.ARTICLES_FETCHED';
and do something like this
import types from './actionTypes'
Will it work the same way as the above code?
Will it work the same way as the above code?
No, types would be equal to 'articles.ARTICLES_FETCHED'
On the other hand, this module:
export default {ARTICLES_FETCHED: 'articles.ARTICLES_FETCHED'}
would act the same as this module:
export const ARTICLES_FETCHED = 'articles.ARTICLES_FETCHED'
The main benefit from using import * as myVar from 'module' is that you get all the exports from module wrapped up in a neat variable myVar.

Confusion about functional equivalency of `export` usage

Shouldn't
import * as convict from "convict";
const config = convict({ ... });
// Perform validation
config.validate({ "allowed": "strict" });
export = config;
be functionally equivalent to:
import * as convict from "convict";
export const config = convict({ ... });
// Perform validation
config.validate({ "allowed": "strict" });
The first snippet works, but the second snippet introduces type errors such as:
TypeError: config.get is not a function
When imported using:
import * as config from "./config";
(This question and Frequent issue with TypeScript and preferring import over require are different. This question is about exports and what should be two equivalent usages. The other question is about imports.)

export const config = ... is so called "named export", it adds config variable to the list of names exported by the module. You can look at various variants of es6 export statement here, this particular one corresponds to the 4th line of the first example (note 'also var, const' comment):
export let name1 = …, name2 = …, …, nameN; // also var, const
and can be used with "named import* like
import {config} from '...';
export = config is entirely different, it's typescript-only export assignment. The documentation says that is should be imported as import config = require(...) which is again typescript-only special syntax.
With current version of TypeScript, export assignment can also be imported as
import * as config from 'module';
but there is breaking change in the works, in the future (maybe as soon as 2.8) this import will stop working with export assingment and will have to be written as
import config from 'module';

The two are indeed different. Essentially, it all has to do with the fact that in the second case config is a named export.
The first snippet produces an export that is just the config. If you did require("./config"), you'd get that config object. This is because you set the exports object to the config. That's why you have to do * as config when importing, because the entire imported object is what you're looking to get.
The second snippet produces an object with a named config field that points to your config; this is equivalent (ish) to doing:
exports = {
config: convict({ ... })
};
In this example, config is a named export. To import it, you'd have to get the config field of the exported object:
import { config } from "./config";