Node.js is a runtime environment for developing
applications in JavaScript outside of the browser. Node.js is most commonly used
in a
command-line interface
to build command-line applications or web servers. After installing Node.js, you
are able to execute a JavaScript file with Node.js using the node command
followed by the name of the file.
Example:
node myJavaScriptFile.jsThe JavaScript contained in the file executed in a Node.js environment should be
similar to a JavaScript file written for the browser. You have access by default
to all of JavaScript's primitives, standard libraries like Math and Date,
and newer versions of Node.js include many
ES6/ES2015+ features like Template Literals, Arrow
Functions, and Destructuring. (oh, yeah!)
However, since there isn't a visual interface defined in Node.js, there are some things that you may be used to being available in a browser, but are not available in Node.js. These features are called Web APIs.
For example, in a browser environment, there is a global document object that
has methods for interfacing the Document Object Model (DOM). Without a visual
interface, the DOM is not available so this object does not exist.
Additionally, in a browser, you can create an alert popup box with
alert('This is an alert message'). Again, since there is no ability to "popup"
in the terminal, the alert function is not available.
One feature that is commonly used for feedback of command-line applications
written in Node.js is the
console methods
like console.log. While the global console object is considered a
Web API, it has
been reimplemented in Node.js for convenient access to the terminal output. In other words,
it works pretty much exactly like it does in the front-end, but it outputs to your terminal,
not your dev tools' console. It uses the terminal's standard output stream, which we will talk about very soon.
Adding the operation console.log('This is a log message') will output
This is a log message to the terminal through the stdout interface along with
an invisible Newline character \n
for any additional commands that may follow.
For this exercise you will create a Hello World program.
Create a JavaScript file to act as a Node.js program named hello-world.js. The file
should contain JavaScript code to output the phrase "Hello, World!" to the
terminal through the stdout stream.
Expected:
$ node hello-world.js
Hello, World!