JavaScript on the Command Line

You can run non-browser specific JavaScript code from the command-line using the node runtime.

Running node to interactively run JavaScript

If you simply run node at the command line you will be in a REPL (Read Evaluate Print Loop) and you can type JavaScript code that is evaluated as you type. This is much like the Console tab in your browser's developers tools.

node

To exit this mode, press Control-D

Running an existing script

If you have a script such as program.js you can run it via:

node program.js

Your code in program.js will be executed and will run until the program experiences an unhandled exception or the script terminates.

Passing arguments to the script

If your script needs information from the user they can specify it on the command line.

Let's say your program intends to add two numbers together and you'd like them to input those on the command line:

node program.js 999 42

When your program runs each space-separated option from the command line are available as an array: process.argv

// process.argv[0] will be node
// process.argv[1] will be the name of your script file
// process.argv[2] will be the first real argument the user supplies, and so on
const firstNumberToAdd = parseInt(process.argv[2])
const secondNumberToAdd = parseInt(process.argv[3])
console.log(`The answer is ${firstNumberToAdd + secondNumberToAdd}`)