Import a JSON file in JavaScript and Node.js (ES6 Modules)

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Borislav Hadzhiev

Last updated: Jan 14, 2023
6 min

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# Table of Contents

  1. Import a JSON file in the Browser
  2. Import a JSON file in Node.js

If you need to import a JSON file in Node.js, click on the second subheading.

If you need to import a JSON file in TypeScript, check out my other article:

# Import a JSON file in the Browser

To import a JSON file in JavaScript:

  1. Make sure the type attribute on the script tag is set to module.
  2. Use an import assertion to import the JSON file.
  3. For example, import myJson from './example.json' assert {type: 'json'}.

Here is my index.html file that has a script tag pointing to an index.js module.

index.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <div id="box">Hello world</div> <!-- ๐Ÿ‘‡๏ธ type set to module --> <script type="module" src="index.js"></script> </body> </html>

Make sure the type attribute is set to module because we are using the ES6 Modules syntax.

And here is how we would import a JSON file in our index.js file.

index.js
import myJson from './example.json' assert {type: 'json'}; // ๐Ÿ‘‡๏ธ { // name: 'Alice', // country: 'Austria', // tasks: [ 'develop', 'design', 'test' ], // age: 30 // } console.log(myJson.person); console.log(myJson.person.name); // ๐Ÿ‘‰๏ธ "Alice" console.log(myJson.person.country); // ๐Ÿ‘‰๏ธ "Austria"

If you get an error when using the assert keyword, try using with instead.

index.js
import myJson from './example.json' with {type: 'json'}; // ๐Ÿ‘‡๏ธ { // name: 'Alice', // country: 'Austria', // tasks: [ 'develop', 'design', 'test' ], // age: 30 // } console.log(myJson.person); console.log(myJson.person.name); // ๐Ÿ‘‰๏ธ "Alice" console.log(myJson.person.country); // ๐Ÿ‘‰๏ธ "Austria"

In March of 2023, the keyword changed from assert to with.

index.js
// Before import myJson from './example.json' assert {type: 'json'}; // after import myJson from './example.json' with {type: 'json'};

However, browsers haven't had time to implement this. For compatibility with existing implementations, the assert keyword is still supported.

The code sample assumes that there is an example.json file located in the same directory.

example.json
{ "person": { "name": "Alice", "country": "Austria", "tasks": ["develop", "design", "test"], "age": 30 } }

The file structure in the example looks as follows.

shell
my-project/ โ””โ”€โ”€ index.html โ””โ”€โ”€ index.js โ””โ”€โ”€ example.json

import json file in the browser

If I open the Console tab in my Developer tools, I can see that the JSON file has been imported successfully.

browser-json-import.webp

You can read more about why this is necessary in the Import assertions proposal page on GitHub.

In short, the import assertion proposal adds an inline syntax for module import statements.

The syntax was introduced for improved security when importing JSON modules and similar module types which cannot execute code.

This helps us avoid a scenario where a server responds with a different MIME type, causing code to be unexpectedly executed.

The assert {type: 'json'} (or with {type: 'json'}) syntax enables us to specify that we are importing a JSON or similar module type that isn't going to be executed.

If I remove the assert {type: 'json'} (or with {type: 'json'}) syntax from the import statement, I'd get an error.

index.js
// โ›”๏ธ Error: Failed to load module script: Expected a JavaScript module script // but the server responded with a MIME type of "application/json". // Strict MIME type checking is enforced for module scripts per HTML spec. import myJson from './example.json';

failed to load module script

You can read more about the import assertions proposal in this tc39 GitHub repository.

# Import a JSON file in Node.js

To import a JSON file in Node.js:

  1. Make sure you are running Node.js version 17.5 or more recent.
  2. Make sure the type property in your package.json file is set to module.
  3. Use an import assertion to import the JSON file.
  4. For example, import myJson from './example.json' assert {type: 'json'}.
Make sure your Node.js version is at least 17.5 because import assertions are valid syntax starting version 17.5.

The type property in your package.json has to be set to module.

package.json
{ "type": "module", // ... rest }

Now we can import a JSON file using an import assertion.

index.js
// ๐Ÿ‘‡๏ธ using assert import myJson from './example.json' assert {type: 'json'}; // ๐Ÿ‘‡๏ธ { // name: 'Alice', // country: 'Austria', // tasks: [ 'develop', 'design', 'test' ], // age: 30 // } console.log(myJson.person); console.log(myJson.person.name); // ๐Ÿ‘‰๏ธ "Alice" console.log(myJson.person.country); // ๐Ÿ‘‰๏ธ "Austria"

import json file in node js

NOTE: if you get an error when using the assert keyword, use the with keyword instead.

index.js
// ๐Ÿ‘‡๏ธ using with import myJson from './example.json' with {type: 'json'}; // ๐Ÿ‘‡๏ธ { // name: 'Alice', // country: 'Austria', // tasks: [ 'develop', 'design', 'test' ], // age: 30 // } console.log(myJson.person); console.log(myJson.person.name); // ๐Ÿ‘‰๏ธ "Alice" console.log(myJson.person.country); // ๐Ÿ‘‰๏ธ "Austria"

The code snippet above assumes that there is an example.json file located in the same directory.

example.json
{ "person": { "name": "Alice", "country": "Austria", "tasks": ["develop", "design", "test"], "age": 30 } }

Here is the output from running the index.js file.

node import json

In March of 2023, the keyword changed from assert to with.

index.js
// Before import myJson from './example.json' assert {type: 'json'}; // after import myJson from './example.json' with {type: 'json'};

However, browsers and the Node.js team haven't had time to implement this. For compatibility with existing implementations, the assert keyword is still supported.

You can read more about the assert syntax on the Import assertions proposal page.

The import assertion proposal adds an inline syntax for module import statements.

The syntax was introduced for improved security when importing JSON modules and similar module types which cannot execute code.

This helps us avoid a scenario where a server responds with a different MIME type, causing code to be unexpectedly executed.

The assert {type: 'json'} (or with {type: 'json'}) syntax enables us to specify that we are importing a JSON or similar module type that isn't going to be executed.

If I remove the assert {type: 'json'} (or with {type: 'json'}) syntax from the import statement, I'd get an error.

index.js
// โ›”๏ธ TypeError [ERR_IMPORT_ASSERTION_TYPE_MISSING]: // Module "/bobbyhadz-js/example.json" needs an // import assertion of type "json" import myJson from './example.json';

err import assertion type missing

You can read more about the import assertions proposal in this tc39 GitHub repository.

Alternatively, you can use the fs module to open the .json file in Node.js.

# Import a JSON file in Node.js with the fs module

Here is an example of using the fs module to import a JSON file when using Node.js.

This is the example.json file that we'll be importing.

example.json
{ "person": { "name": "Alice", "country": "Austria", "tasks": ["develop", "design", "test"], "age": 30 } }

And this is how we can import and use the JSON file in an index.js file.

index.js
import fs from 'fs'; // ๐Ÿ‘‡๏ธ if you use CommonJS imports, use this instead // const fs = require('fs'); const result = JSON.parse(fs.readFileSync('./example.json')); // ๐Ÿ‘‡๏ธ { // name: 'Alice', // country: 'Austria', // tasks: [ 'develop', 'design', 'test' ], // age: 30 // } console.log(result); console.log(result.person.name); // ๐Ÿ‘‰๏ธ "Alice" console.log(result.person.country); // ๐Ÿ‘‰๏ธ "Austria"

The code sample assumes that the example.json file is placed in the same directory as the index.js file.

We used the readFileSync method to read the file synchronously and then used the JSON.parse method to parse the JSON string into a native JavaScript object.

If you use the CommonJS require() syntax, use the following import statement instead.

index.js
const fs = require('fs'); const result = JSON.parse(fs.readFileSync('./example.json')); // ๐Ÿ‘‡๏ธ { // name: 'Alice', // country: 'Austria', // tasks: [ 'develop', 'design', 'test' ], // age: 30 // } console.log(result); console.log(result.person.name); // ๐Ÿ‘‰๏ธ "Alice" console.log(result.person.country); // ๐Ÿ‘‰๏ธ "Austria"

The code sample achieves the same result but uses the require() syntax to import the fs module.

You can also use the await keyword to await a promise when importing the JSON file in more recent versions of Node.js.

index.js
import fs from 'fs/promises'; const result = JSON.parse(await fs.readFile('./example.json')); // ๐Ÿ‘‡๏ธ { // name: 'Alice', // country: 'Austria', // tasks: [ 'develop', 'design', 'test' ], // age: 30 // } console.log(result); console.log(result.person.name); // ๐Ÿ‘‰๏ธ "Alice" console.log(result.person.country); // ๐Ÿ‘‰๏ธ "Austria"

However, note that using await outside an async function is only available starting with Node.js version 14.8+.

If you need to import a JSON file in TypeScript, check out my other article: How to Import a JSON file in TypeScript.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

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