# How To Replace A String In A File Using Node.js

Replacing a string in Node.js is not easy with beginners if they don’t have much knowledge about it. In this article we will help you replace a string in a file in Node.js with the replace method. Let’s learn about it with the explanation and examples below.

## What is a string in JavaScript?

Like many programming languages, String is the most important type in JavaScript. A string is a sequence of characters. Strings in JavaScript are surrounded by either single quotation marks or double quotation marks.

Look at the example below to know more about it.

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript String</h2>

<p id="demo"></p>

<script>

// create a string named 'str1' with single quotation marks.
let str1 = 'Hello everyone, this guide will help you learn how to replace a string in a file by Node.js.'

// create a string named 'str1' with single quotation marks.
let str2 =" I am crvt4722."

// create a string named 'str3' by object String.
let str3 = new String(" Date: 11/09/2022.")

document.getElementById("demo").innerHTML = str1+str2+str3;
</script>

</body>
</html>

Ouput

## Replace A String In A File Using Node.js

The following line is the content of the data_text.txt file.

Learn To Share IT.

And you want to replace “Learn To Share” With “Know”. Let’s learn about it with the explanation below.

### Step 1: Read the file by fs.readFile method

Syntax

fs.readFile( filename, encoding, callback_function )

Parameters

• filename: The name or the path of the file you want to read.
• encoding: The encoding of the file.
• callback_function: It is called after reading the file.

Return Value

It returns the contents/data stored in the file or errors if any.

Look at the example below to know more about the fs.readFile() method.

const fs = require('fs')

fs.readFile('data_text.txt', 'utf-8', (err, data) => {
if (err)    return console.error(err)
console.log(data)
});
console.log(‘Done!’)

Output

Learn To Share IT
Done!


### Step 2: Use replace method to replace a string in a file

Syntax

str.replace(oldValue,newValue)

Parameters

• str: The contents of the file you read before.
• oldValue: The String you want to change.
• newValue: The String you want to replace with.

Return Value

A new string is replaced.

Look at the example below to learn more about replace() method.

const newString = data.replace(/Learn To Share/gi, 'Know')
console.log(newString)

Output

Know IT

### Step 3: Write the content back to the file by writeFile() method

Syntax

fs.writeFile(path, data, encoding, callback)

Parameters

• path: The name or the path of the file.
• data: The contents you want to write.
• encoding: The encoding of the data.
• callback:  It is called after writing the file.

Look at the example below to know more about the writeFile() method.

fs.writeFile('data_text.txt', newString, 'utf-8', err2 => {
if (err2) {
console.log(err2)
}
})

## Summary

There are three steps to replace a string in a file using Node.js. Follow the guide above to solve this problem. We hope this tutorial is helpful to you. Thanks!

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