Typescript load json file

Mastering JSON File Reading in Node.js with TypeScript: A Comprehensive Guide

Learn how to read and import JSON files in Node.js using TypeScript with our comprehensive guide. Access local files, import arrays, and more. Start today!

• Accessing JSON files in a TypeScript way
• Reading a local JSON file in TypeScript
• Part16: WebdriverIO with TypeScript
• Importing an array from a JSON file in TypeScript
• Reading and writing JSON files in Node.js
• Importing a JSON file in TypeScript
• Other code examples for reading JSON files in Node.js with TypeScript
• Conclusion
• How do I read a JSON file in TypeScript?
• How to read a JSON file in nodejs?
• Can we import JSON file in TypeScript?
• How to read JSON data from JSON file in JavaScript?

Node.js and TypeScript are popular tools for developing web applications. JSON files are a popular way to store and exchange data in web development. This guide will provide a comprehensive walkthrough on how to read and import JSON files in Node.js using TypeScript.

Accessing JSON files in a TypeScript way

Before we dive into reading and importing JSON files in Node.js using TypeScript, let’s understand the purpose of typing files in TypeScript. Typing files in TypeScript are used to provide type information for JavaScript code. TypeScript uses these files to provide type information for external libraries or modules that you use in your TypeScript code.

Ensure that the typings.d.ts location is the same as the include property. This will allow TypeScript to automatically recognize the types in the typings file.

Reading a local JSON file in TypeScript

To read a JSON file in Node.js using TypeScript, we can use the FileReader to read the file as text and then use Json.Parse to convert the text into a JSON object. Here’s an example of how to read a local JSON file in TypeScript.

import fs from 'fs';const readFile = (filePath: string) => < const file = fs.readFileSync(filePath, 'utf8'); return JSON.parse(file); >const data = readFile('./data.json'); console.log(data); 

In the above example, we use the fs module to read the file synchronously. We then parse the file using JSON.parse() to convert the text into a JSON object.

Part16: WebdriverIO with TypeScript

Importing an array from a JSON file in TypeScript

We can also import a JSON file in Node.js using TypeScript like any other CommonJS module. We can use the Node.js require() call to import the JSON file. Here’s an example of how to import an array from a JSON file in TypeScript.

const data = require('./data.json'); console.log(data); 

In the above example, we use the require() call to import the JSON file. We then use the imported data as a regular JavaScript object.

Reading and writing JSON files in Node.js

We can use the fs module to interact with the filesystem in Node.js. Here’s an example of how to read and write JSON files in Node.js using TypeScript.

import fs from 'fs';const readFile = (filePath: string) => < const file = fs.readFileSync(filePath, 'utf8'); return JSON.parse(file); >const writeFile = (filePath: string, data: any) => < fs.writeFileSync(filePath, JSON.stringify(data)); >const data = readFile('./data.json'); data.push(< name: 'John Doe', age: 30 >); writeFile('./data.json', data); 

In the above example, we use the readFileSync() method to read the JSON file synchronously. We then use the writeFileSync() method to write the updated data back to the file.

Importing a JSON file in TypeScript

We can also import a JSON file in TypeScript by setting resolveJsonModule to true in our tsconfig.json file and setting esModuleInterop to true. Here’s an example of how to import a JSON file in TypeScript.

import data from './data.json';console.log(data); 

In the above example, we set resolveJsonModule to true and esModuleInterop to true in our tsconfig.json file. We then use a regular import statement to import the JSON file.

Other code examples for reading JSON files in Node.js with TypeScript

In Javascript , for example, write json file nodejs code sample

const fs = require('fs'); const path = require('path');let student = < name: 'Mike', age: 23, gender: 'Male', department: 'English', car: 'Honda' >; fs.writeFileSync(path.resolve(__dirname, 'student.json'), JSON.stringify(student)); 

In Javascript , for example, typescript read json file code example

"resolveJsonModule": true, "esModuleInterop": true, 

In Javascript as proof, typescript read json file code example

import from "config.json"; config.targetKey // this requires `"resolveJsonModule": true` in tsconfig.json

Conclusion

Reading and importing JSON files in Node.js using TypeScript can be achieved in various ways. Understanding the different options available and selecting the best approach for your project is crucial. By following this guide, you should now have a comprehensive understanding of how to read and import JSON files in Node.js using TypeScript.

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Typescript load json file

Last updated: Jan 22, 2023
Reading time · 3 min

# Import a JSON file in TypeScript

To import a JSON file in TypeScript:

1. Set resolveJsonModule to true in your tsconfig.json file.
2. Set esModuleInterop to true in tsconfig.json .
3. Import the JSON file as import employee from ‘./employee.json’ .

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 "compilerOptions":  // . other options "esModuleInterop": true, "resolveJsonModule": true > > 

Here is the JSON file we will import into a TypeScript file.

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 "id": 1, "name": "Bobby Hadz", "salary": 50, "years": [2022, 2023, 2024] > 

# Specify the correct path when importing the JSON file

And here is how we import the JSON file into an index.ts file.

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import employee from './employee.json'; // 👇️ "BOBBY HADZ" console.log(employee.name.toUpperCase()); // 👇️ [2022, 2023, 2024] console.log(employee.years); 

Make sure to correct the path to the employee.json file if you have to.

The example above assumes that the employee.json file and index.ts are located in the same directory.

For example, if your employee.json file was one directory up, you would import it as import employee from ‘../employee.json’ .

# Set moduleResolution to node in your tsconfig.json file

If you get an error, try setting moduleResolution to node in your tsconfig.json file.

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 "compilerOptions":  // . other settings "moduleResolution": "node", "esModuleInterop": true, "resolveJsonModule": true > > 

You should also make sure that the JSON file you are importing is located under your rootDir.

For example, the rootDir setting in my tsconfig.json is set to src . Therefore the json file I am importing has to be located under the src directory.

If your json file is not under your rootDir , you would get an error: «File is not under ‘rootDir’. ‘rootDir’ is expected to contain all source files.».

If you are still unable to import the JSON file, try importing it as follows.

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import * as employee from './employee.json'; // 👇️ "BOBBY HADZ" console.log(employee.name.toUpperCase()); // 👇️ [2022, 2023, 2024] console.log(employee.years); 

The esModuleInterop option is set to false by default, which causes it to treat CommonJS modules similar to ES6 modules. This causes some issues.

Setting esModuleInterop to true fixes these issues.

The resolveJSONModule option allows us to import modules with .json extension in our TypeScript files.

# The JSON import is automatically typed correctly

The resolveJSONModule option is set to false by default, so make sure to set it to true in your tsconfig.json file.

If the option is set to false , you would get an error — «Cannot find module ‘./employee.json’. Consider using ‘—resolveJsonModule’ to import module with ‘.json’ extension.ts(2732)».

This setting also generates a type for the import based on the static JSON shape and enables autocomplete in your IDE.

The rootDir option points to the longest common path of all non-declaration input files.

The setting enforces that all files that need to be emitted are under the rootDir path. Therefore your .json file has to be under the specified rootDir for the import to work.

# Specifying different types for the import JSON file

If you need to specify different types for the imported JSON object, use a type assertion.

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import emp from './employee.json'; type Employee =  id: number; name: string; salary: number; years: number[]; >; const employee = emp as Employee; console.log(employee.id); console.log(employee.name); console.log(employee.salary); console.log(employee.years); 

Type assertions are used when we have information about the type of a value that TypeScript can’t know about.

The employee variable is now of type Employee , so we can access all properties an Employee has on the variable.

# Additional Resources

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

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

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Importing JSON Modules in TypeScript

TypeScript 2.9 introduced a new —resolveJsonModule compiler option that lets us import JSON modules from within TypeScript modules.

#Importing JSON Modules via require Calls

Let’s assume we have a Node application written in TypeScript, and let’s say that we want to import the following JSON file:

In Node, we can use a require call to import this JSON file like any other CommonJS module:

const config = require("./config.json");

The JSON is automatically deserialized into a plain JavaScript object. This allows us to easily access the properties of our config object:

"use strict"; const express = require("express"); const config = require("./config.json"); const app = express(); app.listen(config.server.nodePort, () =>  console.log(`Listening on port $config.server.nodePort> . `); >);

#Importing JSON Files via Static import Declarations

Let’s now say we want to use native ECMAScript modules instead of CommonJS modules. This means we’ll have to convert our require calls to static import declarations:

// We no longer need the "use strict" directive since // all ECMAScript modules implicitly use strict mode.  import * as express from "express"; import * as config from "./config.json"; const app = express(); app.listen(config.server.nodePort, () =>  console.log(`Listening on port $config.server.nodePort> . `); >);

Now, we get a type error in line 2. TypeScript doesn’t let us import a JSON module out of the box, just like that. This was a conscious design decision made by the TypeScript team: pulling in large JSON files could potentially consume a lot of memory, which is why we need to opt into that feature by enabling the —resolveJsonModule compiler flag:

Having people to consciously opt into this would imply the user understands the cost.

Let’s head over to our tsconfig.json file and enable the resolveJsonModule option there:

 "compilerOptions":  "target": "es2015", "module": "commonjs", "strict": true, "moduleResolution": "node", "resolveJsonModule": true  > >

With —resolveJsonModule enabled, we no longer get a type error in our TypeScript file. Even better, we now get type checking and autocompletion!

If we compile our TypeScript file with the compiler options shown above, we get the following JavaScript output:

"use strict"; Object.defineProperty(exports, "__esModule", < value: true >); const express = require("express"); const config = require("./config.json"); const app = express(); app.listen(config.server.nodePort, () =>  console.log(`Listening on port $config.server.nodePort> . `); >);

Notice that the output is pretty much identical to our initial require version:

"use strict"; const express = require("express"); const config = require("./config.json"); const app = express(); app.listen(config.server.nodePort, () =>  console.log(`Listening on port $config.server.nodePort> . `); >);

And there you go! This is how to import JSON modules from within TypeScript modules, only one compiler option away.

This article and 44 others are part of the TypeScript Evolution series. Have a look!

Advanced TypeScript Fundamentals

A deep dive into the fundamnetals of TypeScript’s type system. Learn about the optional chaining ( ?. ) and nullish coalescing ( ?? ) operators, assertion functions, truly private class fields, conditional types, template literal types, adn more.

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