In this tutorial, How to read and write a properties file content in Nodejs Application.

Usually, Properties files are used to store environment information as well as settings related to users or the environment.

Nodejs has a properties-reader npm library to read and write the property files.

  • Create a folder nodejs-reader
  • Inside a folder, Run npm init command to create a nodejs scaffolding application
npm init -Y

This will create a basic nodejs folder Next, Install properties-reader npm library

npm install properties-reader

Let’s see an read and write properties file in the nodejs application

Read properties file in Nodejs Application

In this example, you will learn how to Read key and its values from a properties file and display it to console

Let’s declare the properties file

database=mysql
hostname=localhost
username=john
password=

Here is an example and step by sep

  • Create a new javascript file - propertiesreader.js
  • import properties-reader module into javascript using the required method.
  • Create an object for PropertiesReader by giving properties file location
  • This object has all properties keys and values
  • You can get value using the get method with the given key and print to console.

propertiesreader.js:

var PropertiesReader = require('properties-reader');
var properties = PropertiesReader('config/database.properties');

console.log(properties.get("database"));
console.log(properties.get("hostname"));
console.log(properties.get("username"));
console.log(properties.get("password"));

Output:

mysql
localhost
john
  • How to iterate or loop all keys and values in a properties file?

It has each method to iterate all objects in a file

properties.each((key, value) => {
    console.log(key + ":" + value);
});

Output:

database:mysql
hostname:localhost
username:john
password:

How to write keys and values to a properties file in javascript

These example examples read properties in java with line by line

  • created a File object with an absolute path
  • Create BufferedReader using FileReader object
  • get the First line of the properties file using readLine of BufferedReader
  • Loop using while loop until the end of the line reached
  • Print each line
var PropertiesReader = require('properties-reader');
const propertiesPah = "config/database.properties";
const properties = PropertiesReader(propertiesPah, { writer: { saveSections: true } });

properties.set("key1", "value1")
properties.set("database", "postgres")
properties.save(propertiesPah, function then(err, data) {
    if (err) {
        console.log("error in write a properties file")

    }
    console.log("saved data to properties file")

});

How to write a key and values to a properties file in java

In this example, You can read and write a property using

  • Import PropertiesReader into javascript
  • Create a writer object using PropertiesReader with path and writer object
    • You can add new properties or update existing properties if the properties file exists
  • set method do update or add key and values
  • save method of the properties object writes to the properties file.

Here is a complete example read and write a properties file

var PropertiesReader = require('properties-reader');
const propertiesPath = "config/database.properties";
const writer = PropertiesReader(propertiesPath, { writer: { saveSections: true } });

console.log(writer.get("database"));
console.log(writer.get("hostname"));
console.log(writer.get("username"));
console.log(writer.get("password"));

writer.each((key, value) => {
    console.log(key + ":" + value);
});

writer.set("key1", "value1")
writer.set("database", "value1")

writer.save(propertiesPath, function then(err, data) {
    if (err) {
        console.log("error in write a properties file")

    }
    console.log("saved data to properties file")

});

The output of an file

database=postgres
hostname=localhost
username=john
password=
key1=value1

Conclusion

You learned to read a properties file with keys and values as well and also write keys and values to a properties file in NodeJS javascript application