Develop Reference

Why is my redux store not able to be imported? getting error: "export 'store' was not found in '../../store' [duplicate]

File: SafeString.js
// Build out our basic SafeString type
function SafeString(string) {
this.string = string;
}
SafeString.prototype.toString = function() {
return "" + this.string;
};
export default SafeString;
I have never seen export default before. Are there any equivalent stuff for export default that can be easier to understand?

It's part of the ES6 module system, described here. There is a helpful example in that documentation, also:
If a module defines a default export:
// foo.js
export default function() { console.log("hello!") }
then you can import that default export by omitting the curly braces:
import foo from "foo";
foo(); // hello!
Update: As of June 2015, the module system is defined in §15.2 and the export syntax in particular is defined in §15.2.3 of the ECMAScript 2015 specification.

export default is used to export a single class, function or primitive from a script file.
The export can also be written as
export default function SafeString(string) {
this.string = string;
}
SafeString.prototype.toString = function() {
return "" + this.string;
};
This is used to import this function in another script file
Say in app.js, you can
import SafeString from './handlebars/safe-string';
A little about export
As the name says, it's used to export functions, objects, classes or expressions from script files or modules
Utiliites.js
export function cube(x) {
return x * x * x;
}
export const foo = Math.PI + Math.SQRT2;
This can be imported and used as
App.js
import { cube, foo } from 'Utilities';
console.log(cube(3)); // 27
console.log(foo); // 4.555806215962888
Or
import * as utilities from 'Utilities';
console.log(utilities.cube(3)); // 27
console.log(utilities.foo); // 4.555806215962888
When export default is used, this is much simpler. Script files just exports one thing.
cube.js
export default function cube(x) {
return x * x * x;
};
and used as
App.js
import Cube from 'cube';
console.log(Cube(3)); // 27

What is “export default” in JavaScript?
In default export the naming of import is completely independent and we can use any name we like.
I will illustrate this line with a simple example.
Let’s say we have three modules and an index.html file:
modul.js
modul2.js
modul3.js
index.html
File modul.js
export function hello() {
console.log("Modul: Saying hello!");
}
export let variable = 123;
File modul2.js
export function hello2() {
console.log("Module2: Saying hello for the second time!");
}
export let variable2 = 456;
modul3.js
export default function hello3() {
console.log("Module3: Saying hello for the third time!");
}
File index.html
<script type="module">
import * as mod from './modul.js';
import {hello2, variable2} from './modul2.js';
import blabla from './modul3.js'; // ! Here is the important stuff - we name the variable for the module as we like
mod.hello();
console.log("Module: " + mod.variable);
hello2();
console.log("Module2: " + variable2);
blabla();
</script>
The output is:
modul.js:2:10 -> Modul: Saying hello!
index.html:7:9 -> Module: 123
modul2.js:2:10 -> Module2: Saying hello for the second time!
index.html:10:9 -> Module2: 456
modul3.js:2:10 -> Module3: Saying hello for the third time!
So the longer explanation is:
'export default' is used if you want to export a single thing for a module.
So the thing that is important is "import blabla from './modul3.js'" - we could say instead:
"import pamelanderson from './modul3.js" and then pamelanderson();. This will work just fine when we use 'export default' and basically this is it - it allows us to name it whatever we like when it is default.
P.S.: If you want to test the example - create the files first, and then allow CORS in the browser -> if you are using Firefox type in the URL of the browser: about:config -> Search for "privacy.file_unique_origin" -> change it to "false" -> open index.html -> press F12 to open the console and see the output -> Enjoy and don't forget to return the CORS settings to default.
P.S.2: Sorry for the silly variable naming
More information is in link2medium and link2mdn.

export default function(){} can be used when the function doesn't have a name. There can only be one default export in a file. The alternative is a named export.
This page describes export default in detail as well as other details about modules that I found very helpful.

As explained on this MDN page
There are two different types of export, named and default. You can
have multiple named exports per module but only one default
export[...]Named exports are useful to export several values. During
the import, it is mandatory to use the same name of the corresponding
object.But a default export can be imported with any name
For example:
let myVar; export default myVar = 123; // in file my-module.js
import myExportedVar from './my-module' // we have the freedom to use 'import myExportedVar' instead of 'import myVar' because myVar was defined as default export
console.log(myExportedVar); // will log 123

There are two different types of export, named and default. You can have multiple named exports per module but only one default export. Each type corresponds to one of the above.
Source: MDN
Named Export
export class NamedExport1 { }
export class NamedExport2 { }
// Import class
import { NamedExport1 } from 'path-to-file'
import { NamedExport2 } from 'path-to-file'
// OR you can import all at once
import * as namedExports from 'path-to-file'
Default Export
export default class DefaultExport1 { }
// Import class
import DefaultExport1 from 'path-to-file' // No curly braces - {}
// You can use a different name for the default import
import Foo from 'path-to-file' // This will assign any default export to Foo.

In my opinion, the important thing about the default export is that it can be imported with any name!
If there is a file, foo.js, which exports default:
export default function foo(){}
it can be imported in bar.js using:
import bar from 'foo'
import Bar from 'foo' // Or ANY other name you wish to assign to this import

Export Default is used to export only one value from a file which can be a class, function, or object. The default export can be imported with any name.
//file functions.js
export default function subtract(x, y) {
return x - y;
}
//importing subtract in another file in the same directory
import myDefault from "./functions.js";
The subtract function can be referred to as myDefault in the imported file.
Export Default also creates a fallback value which means that if you try to import a function, class, or object which is not present in named exports. The fallback value given by default export will be provided.
A detailed explanation can be found on https://developer.mozilla.org/en-US/docs/web/javascript/reference/statements/export

One of the good features introduced in ES6 was javascript modules in an efficient way by which we can export and import variables, functions, and classes between different .js files.
We have two different ways to export: Named exports and Default exports. To properly understand the default export, we must first understand the named export well.
Named export
In this case, in the source file, we export the desired variables, functions, or classes that have a specific name. The syntax is as follows:
// file: source.js
export const myVariable = /* … */
export function myFunction() { /* … */ }
export class myClass { /* … */ }
Now, to access the above items in the target file, we must import them as follows:
// file: target.js (in the same directory as the source.js file)
import { myVariable } from "./source.js"
import { myFunction } from "./source.js"
import { myClass } from "./source.js"
Now it's time to get to the main question "what exactly is the default export"?
Default export
Except for the cases where we exported them by name (named exports), there is a similar feature called default export that can be used only once in each .js file. See the following example and compare it with the previous source.js file:
// file: source.js
export default function myNewFunction() { /* … */ }
export const myVariable = /* … */
export function myFunction() { /* … */ }
export class myClass { /* … */ }
In fact, each .js file can have "multiple named exports" and "only one default export"_ here myNewFunction is exported as default. With this, when importing in the target file, javascript understands which item is exported as default.
The item that is "exported as default" (myNewFunction) is imported in the target.js file as follows:
// file: target.js (in the same directory as the source.js file)
import anyName from "./source.js"
Look carefully at the differences! Here, we don't have { } sign after import, and we used a custom name that we didn't have in the source file. Here anyName represents myNewFunction.
This shows that we can give "any desired name" to the item that is "exported as default" when importing it and just pointing to the "path" of the source file, JavaScript will find that file and import it.
Some important notes:
Unlike named exports, in default export we don't need to export named
items and we can export "unnamed" items as well.
Why did they add the Default export feature to ES6 at all!? for the ability
to export "unnamed items" (anonymous functions and classes) as well as
expressions and even object literals in addition to named items.

In ES6 there are two kinds of exports:
Named exports - for example export function func() {} is a named export with the name of func. Named modules can be imported using import { exportName } from 'module';. In this case, the name of the import should be the same as the name of the export. To import the func in the example, you'll have to use import { func } from 'module';. There can be multiple named exports in one module.
Default export - is the value that will be imported from the module, if you use the simple import statement import X from 'module'. X is the name that will be given locally to the variable assigned to contain the value, and it doesn't have to be named like the origin export. There can be only one default export.
A module can contain both named exports and a default export, and they can be imported together using import defaultExport, { namedExport1, namedExport3, etc... } from 'module';.

export default is used to export a single class, function or primitive.
export default function() { } can be used when the function has no name. There can only be one default export in a file.
Read more

Why do we have to use “*” while importing in typescript? [duplicate]

What is the difference in TypeScript between export and default export?
In all the tutorials, I see people exporting their classes and I cannot compile my code if I don't add the default keyword before exporting.
Also, I couldn't find any trace of the default export keyword in the official TypeScript documentation.
export class MyClass {
collection = [1,2,3];
}
Does not compile. But:
export default class MyClass {
collection = [1,2,3];
}
Does.
The error is:
error TS1192: Module '"src/app/MyClass"' has no default export.

Default Export (export default)
// MyClass.ts -- using default export
export default class MyClass { /* ... */ }
The main difference is that you can only have one default export per file and you import it like so:
import MyClass from "./MyClass";
You can give it any name you like. For example this works fine:
import MyClassAlias from "./MyClass";
Named Export (export)
// MyClass.ts -- using named exports
export class MyClass { /* ... */ }
export class MyOtherClass { /* ... */ }
When you use a named export, you can have multiple exports per file and you need to import the exports surrounded in braces:
import { MyClass } from "./MyClass";
Note: Adding the braces will fix the error you're describing in your question and the name specified in the braces needs to match the name of the export.
Or say your file exported multiple classes, then you could import both like so:
import { MyClass, MyOtherClass } from "./MyClass";
// use MyClass and MyOtherClass
Or you could give either of them a different name in this file:
import { MyClass, MyOtherClass as MyOtherClassAlias } from "./MyClass";
// use MyClass and MyOtherClassAlias
Or you could import everything that's exported by using * as:
import * as MyClasses from "./MyClass";
// use MyClasses.MyClass and MyClasses.MyOtherClass here
Which to use?
In ES6, default exports are concise because their use case is more common; however, when I am working on code internal to a project in TypeScript, I prefer to use named exports instead of default exports almost all the time because it works very well with code refactoring. For example, if you default export a class and rename that class, it will only rename the class in that file and not any of the other references in other files. With named exports it will rename the class and all the references to that class in all the other files.
It also plays very nicely with barrel files (files that use namespace exports—export *—to export other files). An example of this is shown in the "example" section of this answer.
Note that my opinion on using named exports even when there is only one export is contrary to the TypeScript Handbook—see the "Red Flags" section. I believe this recommendation only applies when you are creating an API for other people to use and the code is not internal to your project. When I'm designing an API for people to use, I'll use a default export so people can do import myLibraryDefaultExport from "my-library-name";. If you disagree with me about doing this, I would love to hear your reasoning.
That said, find what you prefer! You could use one, the other, or both at the same time.
Additional Points
A default export is actually a named export with the name default, so if the file has a default export then you can also import by doing:
import { default as MyClass } from "./MyClass";
And take note these other ways to import exist:
import MyDefaultExportedClass, { Class1, Class2 } from "./SomeFile";
import MyDefaultExportedClass, * as Classes from "./SomeFile";
import "./SomeFile"; // runs SomeFile.js without importing any exports

I was trying to solve the same problem, but found an interesting advice by Basarat Ali Syed, of TypeScript Deep Dive fame, that we should avoid the generic export default declaration for a class, and instead append the export tag to the class declaration. The imported class should be instead listed in the import command of the module.
That is: instead of
class Foo {
// ...
}
export default Foo;
and the simple import Foo from './foo'; in the module that will import, one should use
export class Foo {
// ...
}
and import {Foo} from './foo' in the importer.
The reason for that is difficulties in the refactoring of classes, and the added work for exportation. The original post by Basarat is in Avoid Export Default

Named export
In TypeScript you can export with the export keyword. It then can be imported via import {name} from "./mydir";. This is called a named export. A file can export multiple named exports. Also the names of the imports have to match the exports. For example:
// foo.js file
export class foo{}
export class bar{}
// main.js file in same dir
import {foo, bar} from "./foo";
The following alternative syntax is also valid:
// foo.js file
function foo() {};
function bar() {};
export {foo, bar};
// main.js file in same directory
import {foo, bar} from './foo'
Default export
We can also use a default export. There can only be one default export per file. When importing a default export we omit the square brackets in the import statement. We can also choose our own name for our import.
// foo.js file
export default class foo{}
// main.js file in same directory
import abc from "./foo";
It's just JavaScript
Modules and their associated keyword like import, export, and export default are JavaScript constructs, not TypeScript. However, TypeScript added the exporting and importing of interfaces and type aliases to it.

Here's an example with simple object exporting.
var MyScreen = {
/* ... */
width : function (percent){
return window.innerWidth / 100 * percent
}
height : function (percent){
return window.innerHeight / 100 * percent
}
};
export default MyScreen
In the main file (use it when you don't want and don't need to create a new instance) and it is not global, you will import this only when it is needed:
import MyScreen from "./module/screen";
console.log(MyScreen.width(100));

Why and when to use default export over named exports in es6 Modules?

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

Re-exporting modules does not work with object spread

i have an index.js file that reads:
import aReducer from './ducks/a';
import bReducer from './ducks/b';
import * as aSelectors from './ducks/a';
import * as bSelectors from './ducks/b';
console.log(aReducer) //function i expect
console.log(aSelectors) //object with keys to selectors i expect
export { aReducer, bReducer, ...aSelectors, ...bSelectors };
If I console.log in this file I see that the reducers are functions I expect and the selectors alias are objects with keys to the selectors I expect. The reducers are default exports for the duck files and the selectors are exports from the same respective file.
However, when I try to import this module with another file I am only able to import the two reducers. The two selectors are undefined. I thought that de-structuring would add each key to my export object. What am I doing wrong?
other_file1.js
import { aReducer, bReducer } from 'my-module'; //works!
other_file2.js
import { someSelectorThatWasInMyaSelectorsObject } from 'my-module'; //does NOT work!

You cannot use ... in an export {}; block. It is an explicit list of names just like import {name} from is. It is not an object with keys being exported. e.g. the same way imports do
import { foo as fooRenamed } from "";
with export it is
export {
fooVar as foo,
};
The export block is an explicit list of variables to export, with an optional explicit name for the export. There are no objects involved.
Specifically, there are no objects involved because the names of the exports are processed and known before the body of the file has even executed, so not only are objects not allowed, they are impossible to allow because objects require execution to exist.
To get what you'd want, you should use:
// Export the referenced files' default under two specific names.
export { default as aReducer } from './ducks/a';
export { default as bReducer } from './ducks/b';
// Re-export every named export from these two files.
export * from './ducks/a';
export * from './ducks/b';

Why do I need to wrap some importings with figure brackets {} in ES6? [duplicate]

This question already has answers here:
`export const` vs. `export default` in ES6
(6 answers)
Closed 6 years ago.
I found a strange situation in ES6. For example, I'm using npm packages react and react-router. I want to import them to the file:
import React from "react";
import { browserHistory } from "react-router";
The strange situation is that I need to wrap browserHistory in figure brackets, but I don't need to wrap React. What is the reason?
import { React } from "react"; // React is undefined
import browserHistory from "react-router"; // browserHistory is undefined
What's the reason that I need to customize my import?

ES6 modules differentiate between two kinds of exports: default exports and other exports.
Every module can have at most one default export. A default export is kind of like the “main attraction” of a module. It’s supposed to be the one thing that you probably meant the module to have. All other exports fit into the other category.
So a module can have any number of exports (even zero), of which at most one can be a default export.
On the export side of the syntax, a default export is simply marked by adding a default after the export keyword:
// this is a normal export
export var foo = 'foo';
// this is a default export
var bar = 'bar';
export default bar;
On the import side of the syntax, this gets a it more complicated: Default exports are imported outside of curly braces. All other exports are imported inside curly braces.
import bar, { foo } from 'some-module';
This would import the default exported member of the module as bar and also import the (named) other export foo. Note that default exports do not have a fixed name: The original name of the member at export time does not matter. Instead, you give it some name when importing it. So you could also write this instead:
import baz, { foo } from 'some-module';
This would still import the same default export from the module, but give it a different name. Other imports however are required to have the correct name, since that’s what’s used to identify them. You can however give them a different name by using the as keyword.
There are a few more things to know when using the export and import statements. You should check MDN for a full description of them.

If the module you are importing has a default export, then you do not have to use the { } syntax to access the given export. Named (non-default) exports must be accessed via the { } syntax. A module can have a default export as well as many named exports.
An example of that would be React which is a default export, but the module also has a named export of Component. To import both of these exports the syntax: import React, { Component } from 'react' would be used.