How to read a File's contents in TypeScript

# 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.

index.ts

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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');

file read successfully

The code for this article is available on GitHub

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.

index.ts

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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');

typescript read file line by line

The code for this article is available on GitHub

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.

example.txt

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bobby
hadz
com

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

shell

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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.

tsconfig.json

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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.

index.ts

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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.

index.ts

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

I've also written an article on how to write to a file using TypeScript.

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.

index.ts

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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');

file read successfully

The code for this article is available on GitHub

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

index.ts

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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');

The code for this article is available on GitHub

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.

example.txt

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bobby
hadz
com

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

index.ts

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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

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How to read a File's contents in TypeScript

# Read a File's contents synchronously in TypeScript

# Read a File's contents asynchronously in TypeScript

# Additional Resources

Borislav Hadzhiev