Import Functions from another file in React

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Borislav Hadzhiev

Last updated: Apr 23, 2022

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Import Functions from another file in React #

To import a function from another file in React:

  1. Export the function from file A, e.g. export function sum() {}.
  2. Import the function in file B as import {sum} from './another-file'.
  3. Use the imported function in file B.

Here is an example of exporting functions from a file called another-file.js.

another-file.js
// 👇️ named export export function sum(a, b) { return a + b; } // 👇️ named export export function multiply(a, b) { return a * b; } // 👇️ (arrow function) // export const sum = (a, b) => { // return a + b; // };

The syntax is the same when using arrow functions. All you have to do is use the export keyword.

Here is how we would import the functions in a file called App.js.

App.js
// 👇️ named import import {sum, multiply} from './another-file'; export default function App() { return ( <div> <h2>5 + 5 = {sum(5, 5)}</h2> <hr /> <h2>10 * 5 = {multiply(10, 5)}</h2> </div> ); }

Make sure to correct the path that points to the another-file.js module if you have to. The example above assumes that another-file.js and App.js are located in the same directory.

For example, if another-file.js was located one directory up, you'd have to import as import {sum} from '../another-file'.

We wrapped the name of the functions in curly braces when importing them - this is called a named import.

The import/export syntax is called JavaScript modules.

In order to be able to import a function from a different file, it has to be exported using a named or default export.

The example above uses a named export and a named import.

The main difference between named and default exports and imports is - you can have multiple named exports per file, but you can only have a single default export.

Let's look at an example of how we would import a function that was exported using a default export.

another-file.js
// 👇️ default export export default function sum(a, b) { return a + b; } // 👇️ arrow functions // const sum = (a, b) => { // return a + b; // } // export default sum;

IMPORTANT: If you are exporting a variable (or an arrow function) as a default export, you have to declare it on 1 line and export it on the next. You can't declare and default export a variable on the same line.

another-file.js
const sum = (a, b) => { return a + b; }; // 👇️ default export (next line) export default sum;

And here is how we would import the function using a default import.

App.js
// 👇️ default import import sum from './another-file'; export default function App() { return ( <div> <h2>5 + 5 = {sum(5, 5)}</h2> </div> ); }

Notice that we didn't wrap the import in curly braces.

We could have also used a different name when importing the function, e.g. foo.

App.js
import foo from './another-file'; export default function App() { return ( <div> <h2>5 + 5 = {foo(5, 5)}</h2> </div> ); }

This works, but is confusing and should be avoided.

In my experience, most real world codebases exclusively use named exports and imports because they make it easier to leverage your IDE for autocompletion and auto-imports.
You also don't have to think about which members are exported with a default or named export.

You can also mix and match, here is an example of a file that uses both - a default and a named export.

another-file.js
// 👇️ default export export default function sum(a, b) { return a + b; } // 👇️ named export export const multiply = (a, b) => { return a * b; };

And here is how you would import the two functions.

App.js
// 👇️ default and named imports import sum, {multiply} from './another-file'; export default function App() { return ( <div> <h2>5 + 5 = {sum(5, 5)}</h2> <hr /> <h2>10 * 5 = {multiply(10, 5)}</h2> </div> ); }

We used a default import to import the sum function and a named import to import the multiply function.

Note that you can only have a single default export per file, but you can have as many named exports as necessary.

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