Read from file typescript

Read Text File In Typescript

/__tests__/**/*.ts», «/src/**/*.d.ts»] Refernce Typescript, declaration files can be indicated., Here is an example of the ‘typings.json’ file., in a directory indicates that the directory is the root of a TypeScript project., all TypeScript (.ts, .d.ts and .tsx) files in the containing directory and subdirectories except those

Write file in typescript

This tutorial is about how to read text files in TypeScript., It offers a wide range of features to deal with a local file system, such as reading from a file, writing, code> module supports both the asynchronous and synchronous APIs to read from a file., It blocks the execution until the file read operation finishes., TypeScript File

Read and write a text file in typescript

Question: How should I read and write a text file from typescript, I am not sure would read/write a file be sandboxed in

Typescript how to read a txt file c

More Examples Read textfile How to read from a text file, Read only a part of a textfile How to only read a part of a TextStream file., Read one line of a textfile How to read one line from a TextStream file., Read all lines from a textfile How to read all the lines from a TextStream file, Skip a line of a textfile How to skip a line when reading the TextStream file.

Typescript how to read file in ionic 5

the path url is correct and you can check if the file, ionic cordova plugin add cordova-plugin-file npm install —save @ionic-native/file, /ngx’; 2.import < File >from ‘@ionic-native/file/ngx’; make instansts in, : File ) put this function in your ts file openPDF, ; The browser might not support window.URL -> read

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Read from file typescript

Last updated: Jan 24, 2023
Reading time · 3 min

# Read a File’s contents synchronously in TypeScript

Use the readFileSync() method to read a file’s contents in TypeScript.

The method takes the path and encoding as parameters and returns the contents of the specified file.

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import  readFileSync > from 'fs'; import  join > from 'path'; function syncReadFile(filename: string)  const result = readFileSync(join(__dirname, filename), 'utf-8'); // bobby // hadz // com console.log(result); return result; > syncReadFile('./example.txt'); 

The function takes a file name and reads the contents of the file synchronously, returning a string.

If you need to get an array of the contents of the file, use the following code sample instead.

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import  readFileSync > from 'fs'; import  join > from 'path'; function syncReadFile(filename: string)  const contents = readFileSync(join(__dirname, filename), 'utf-8'); const arr = contents.split(/\r?\n/); console.log(arr); // 👉️ [ 'bobby', 'hadz', 'com' ] // ✅ Read file line by line arr.forEach((line) =>  // bobby // hadz // com console.log(line); >); return arr; > syncReadFile('./example.txt'); 

You can use the forEach() method to read the contents of the file line by line.

The code sample assumes that you have an example.txt file located in the same directory as the index.ts script.

If you haven’t installed the typings for Node.js, run the following command.

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npm install --save-dev @types/node 

if you get an error that the type declarations for the fs module are not found, add the node string to the types array in your tsconfig.json file.

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 "compilerOptions":  "types": [ "node" ] >, > 

The fs.readFileSync method takes the path to the file as the first parameter and the encoding as the second.

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const result = readFileSync(join(__dirname, filename), 'utf-8'); 

The method returns the contents of the provided path.

If you omit the encoding parameter, the function will return a buffer, otherwise, a string is returned.

The __dirname variable returns the directory name of the current module.

For example, if you use the __dirname variable in a module located at /home/user/my-module.js , the __dirname variable would return /home/user .

We used the path.join method to join the path of the directory of the current module with the provided filename.

The code assumes that there is an example.txt file located in the same directory as the current module.

For example, if the file you’re reading is located one directory up, you’d pass ../example.txt as a parameter to the function.

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syncReadFile('../example.txt'); 

Alternatively, you could use the fsPromises object to read a file asynchronously.

# Read a File’s contents asynchronously in TypeScript

If you need to read a file’s contents asynchronously, use the fsPromises.readFile() method.

The method takes the path and encoding as parameters and asynchronously reads the contents of the file.

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import  promises as fsPromises > from 'fs'; import  join > from 'path'; async function asyncReadFile(filename: string)  try  const result = await fsPromises.readFile( join(__dirname, filename), 'utf-8', ); // bobby // hadz // com console.log(result); return result; > catch (err)  console.log(err); return 'Something went wrong'; > > asyncReadFile('./example.txt'); 

If you need to get an array of the contents of the file, use the following code sample instead.

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import  promises as fsPromises > from 'fs'; import  join > from 'path'; async function asyncReadFile(filename: string)  try  const contents = await fsPromises.readFile( join(__dirname, filename), 'utf-8', ); const arr = contents.split(/\r?\n/); console.log(arr); // 👉️ [ 'bobby', 'hadz', 'com' ] // ✅ Read file line by line arr.forEach((line) =>  // bobby // hadz // com console.log(line); >); return arr; > catch (err)  console.log(err); return 'Something went wrong'; > > asyncReadFile('./example.txt'); 

You can use the forEach() method to read the contents of the file line by line.

The fsPromises.readFile() method asynchronously reads the contents of the provided file.

The code sample assumes that you have an example.txt file located in the same directory as the index.ts script.

For example, if the file you’re reading is located one directory up, you’d pass ../example.txt as a parameter to the function.

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asyncReadFile('../example.txt'); 

If you don’t provide a value for the encoding parameter, the method returns a buffer, otherwise, a string is returned.

The method returns a promise that resolves with the contents of the file, so we have to await it or use the .then() method on it to get the resolved string.

# 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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Reading and Writing Files With TypeScript

By Omari Thompson-Edwards Hey, I’m Omari! I’m a full-stack developer from the UK, with a passion for ReactJS. I’m an enthusiastic and hardworking junior developer, driven by a desire to learn and explore ideas. Published: 13 December 2022

You can read and write files in TypeScript using the “fs” module, which is a Node module containing methods for file system operations. The module is very versatile and provides a lot of different ways of reading from and writing to files, so in this article, I’ll talk you through them.

Reading Files Synchronously

import * as fs from 'fs'; fs.readFileSync('/path-to-file', 'utf-8');

This will synchronously load the file you’ve provided into a string, assuming your file is using UTF-8 encoding. Here’s an example loading in all the possible Wordle words, from a text file:

import * as fs from 'fs'; const words = fs.readFileSync('./words.txt', 'utf-8'); console.log(words); /* aahed aalii aargh aarti abaca abaci aback abacs. etc */

If you look at the type of our variable though, it’s still just one big string. This might be fine for some use cases, but for example, if we were recreating Wordle, we’d want to process this into something we could check words against. Luckily in our case, this is very simple, we just need to split our string by the invisible newline characters:

const words = fs.readFileSync('./words.txt', 'utf-8'); const wordList = words.split('\r\n'); console.log(wordList); /* [ 'aahed', 'aalii', 'aargh', 'aarti', 'abaca', 'abaci', 'aback', 'abacs', 'abaft', 'abaka', 'abamp', 'aband', 'abase', 'abash', 'abask', 'abate', 'abaya', 'abbas', 'abbed', 'abbes', 'abbey', 'abbot', 'abcee', 'abeam', 'abear', 'abele', 'abers', 'abets', . */

Line By Line

Our wordle example is a large text file. For cases like this, you might want to approach the problem line by line. If you’re using a newer version of Node, i.e. something newer than v18.11.0, a new function has been added for this scenario:

import * as fsPromise from 'fs/promises'; const file = await fsPromise.open('./words.txt', 'r'); for await (const line of file.readLines())

We can open the file using fs.open(), the important thing to note here is that we’re using the promise version of this method instead of the synchronous one. This gives us back an interactor which we can iterate through line by line. You can do anything between each iteration. This is a new method however, so just in case you’re still working with an older version of Node, you can use the native module “readline” to accomplish the same thing:

import * as readline from 'readline'; const lineReader = readline.createInterface(< input: fs.createReadStream('./words.txt'), terminal: false, >); lineReader.on('line', (line) => < console.log(line); >); 

Here we’re setting up a stream to load the file in line by line, and an event listener to call a function on each line.

Loading in JSON

If you’re trying to load in JSON at build time, the easiest way to do this is to import it as a module:

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

Your JSON will get imported into a variable, and automatically parsed. This is really useful for use cases like config files, where you know what file you need and where. If for example, you don’t know at build time what JSON you need to read, you can use the “fs” module again to load in your file:

const loadedConfig = fs.readFileSync('./config.json', 'utf-8'); const config = JSON.parse(loadedConfig); console.log(config);

All we need to do after is use JSON.parse() to convert the JSON text into an object. You might notice you get no type inference on this however since TypeScript doesn’t know what’s in your file. All we need to do in this case is cast the result to whatever type we need. In my case I’ve created this type:

const config = JSON.parse(loadedConfig) as Config; config.permissions[0]; //✔️Works config.foo; //️❌Doesn't!

Writing Files

Writing files in TypeScript is equally as simple, using readFileSync()‘s counterpart, writeFileSync():

const myText = 'Hi!\r\n'; fs.writeFileSync('./foo.txt', myText);

const myConfig: Config = < age: 22, name: 'Omari', password: 'potpurri', permissions: ['read'], >; const json = JSON.stringify(myConfig); fs.writeFileSync('./config.json', json); 

Promises

You might have noticed the “Sync” suffix at the end of the functions we’ve been using. This is because these have been the synchronous versions of the fs methods, i.e. they start, and the code waits for them to finish before proceeding. For a lot of use cases, this is probably fine. If you’re working with large files or a lot of files you might want to test out the Promise version and see if it works faster. You can import these with:

import * as fsPromise from 'fs/promises';

 const loadedConfig = await fsPromise.readFile('~/config.json', 'utf-8'); const config = JSON.parse(loadedConfig); const myConfig: Config = < age: 22, name: 'Omari', password: 'potpurri', permissions: ['read'], >; const json = JSON.stringify(myConfig); await fsPromise.writeFile('~/config.json', json);

The methods are nearly identical, other than having to use asynchronous syntax to get the result. And that’s all! Hopefully, I’ve covered your use case, but if not feel free to leave a comment below. Thanks for reading, let me know if you liked this article, or if you ran into any troubles.

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👋 Hey, I’m Omari Thompson-Edwards

Hey, I’m Omari! I’m a full-stack developer from the UK, with a passion for ReactJS. I’m an enthusiastic and hardworking junior developer, driven by a desire to learn and explore ideas.

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