Node.js Hello World

Summary: in this tutorial, you will learn how to build and run the Node.js Hello World program.

Building the Node.js Hello World program #

Step 1. Open your terminal and create a new directory called hello-world:

mkdir hello-worldCopy

Step 2. Navigate to the project directory:

cd hello-worldCopy

Step 3. Create a new file within the project directory named index.js. The index.js file will be the program’s entry point. Please note that you can use any name, such as main.js or server.js.

Step 4. Add the following code to the index. js file:

console.log('Hello, World!');Copy

In the index.js file, we output the message 'Hello, World!' to the console.

Step 5. Run the index.js file by executing the following command in the terminal:

node index.jsCopy

You should see the following output:

Hello, World!Copy

If you see an error instead, the Node.js may not be installed properly on your system.

Adding variables #

Step 1. Modify the code in the index.js file to the following:

const firstName = 'John';
console.log(`Hello, ${firstName}!`);Copy

How it works.

First, declares a constant firstName and initialize its value to 'John':

const firstName = 'John';Copy

Second, embed the value of firstName into a string using a template literal:

`Hello, ${firstName}!`Copy

Third, display the message to the console:

console.log(`Hello, ${firstName}!`);Copy

Step 2. Open the terminal and run the index.js file:

node index.jsCopy

You’ll see the following output:

Hello, John!Copy

Using the –watch flag #

Whenever you change the code, you need to run the command node index.js to execute the program. This isn’t productive because you have to switch between the code editor and the terminal every time.

To automatically rerun the Node.js program whenever the code changes, you can use the --watch flag as follows:

node --watch index.jsCopy

Now, the terminal will automatically rerun index.js whenever you change the code.

Please note that --watch flag has been available since Node.js 18.11.0.

Summary #

• Use the console.log to output a message to the console.
• Run the command node index.js to execute the code in the index.js file.
• Use the --watch flag to automatically rerun the Node.js program whenever the code changes.