what does export default mean code example

Example 1: export and export default

// Three different export styles
export foo;
export default foo;
export = foo;

// The three matching import styles
import {foo} from 'blah';
import foo from 'blah';
import * as foo from 'blah';

Example 2: export default

/*
Since export default is used to declare a fallback value for a module or 
file, you can only have one value be a default export in each module or 
file. Additionally, you cannot use export default with var, let, or const.
*/

// named function
export default function add(x, y) {
  return x + y;
}

// anonymous function
export default function(x, y) {
  return x + y;
}

Example 3: javascript export default

// Exporting individual features
export let name1, name2, …, nameN; // also var, const
export let name1 = …, name2 = …, …, nameN; // also var, const
export function functionName(){...}
export class ClassName {...}

// Export list
export { name1, name2, …, nameN };

// Renaming exports
export { variable1 as name1, variable2 as name2, …, nameN };

// Exporting destructured assignments with renaming
export const { name1, name2: bar } = o;

// Default exports
export default expression;
export default function (…) { … } // also class, function*
export default function name1(…) { … } // also class, function*
export { name1 as default, … };

// Aggregating modules
export * from …; // does not set the default export
export * as name1 from …;
export { name1, name2, …, nameN } from …;
export { import1 as name1, import2 as name2, …, nameN } from …;
export { default } from …;

Example 4: javascript export default

export default const array = [1, 2, 3];
export default let array = [1, 2, 3];
export default var array = [1, 2, 3];
export default const variable = 'value';
export default let variable = 'value';
export default var variable = 'value';
export default const variable;
export default let variable;
export default var variable;
export default function functionName () {
  // ...
}
export default class ClassName {
  // ...
}
// Before you use export default: You can't have 2 or more export default's.