Running JavaScript Shell Script from Node.js

Instead of the usual web browser, this tutorial takes you on the route of using a stand-alone JavaScript shell first to execute JavaScript code. The interpreter chosen here is Node.js.

Detailed instructions on installing Node.js via the package manager can be found following the link below

https://nodejs.org/en/download/package-manager/

To quick test if the installation is correct, check the version of Node.js installed from the terminal

				node -v

In Ubuntu systems, it would be

				nodejs -v

It should give the version number, something like v11.12.0.

After installing Node.js, open a text editor and create a JavaScript file, say, hello.js. Add the following shebang interpreter directive to the file as its first line of script

				
					#!/usr/bin/env node

(In some operating systems, like Ubuntu, this line could be #!/usr/bin/env nodejs.)

As in any other programming language, we start by printing "Hello, World!" into the terminal. To achieve this, we append the line console.log("Hello, World!"); to the file and save it 

				
					#!/usr/bin/env node
					console.log("Hello, World!");

Next, we type a command in the terminal to mark hello.js as executable 

				chmod u+x hello.js

The script file can now be executed from the terminal by running the command 

				./hello.js

Executing Explicitly

The hello.js script file can also be executed explicitly by specifying the Node.js interpreter. Assuming that you are in the same location as hello.js, type

					node hello.js

in the terminal and the script will be executed. If you are in some other location, specify the path to hello.js after the node command.

Notes

  • The .js extension for the script file specifies that the file contains JavaScript code. But in this case, it would have run even with the .sh extension.
  • The location of the Node.js interpreter can be found with the command which node. The shebang interpreter directive could also have have been hardcoded to this path as #!/usr/bin/node instead of #!/usr/bin/env node.
  • The chmod u+x hello.js command is basically to make the file executable. The "u" after "chmod" stands for "user" and "x" for "execute." This can also be achieved via the GUI in most operating systems. For example, in Ubuntu, the equivalent procedure is to right-click on the file, select the Permissions tab, and check Allow executing file as program.