Question

When Node.js is installed on a system, it provides a program called node , which is used to run JavaScript files. Say you have a file hello.js , containing this code:

var message = "Hello world";
console.log(message);

You can then run node from the command line like this to execute the program:

$ node hello.js
Hello world

The console.log method in Node does something similar to what it does in the browser. It prints out a piece of text. But in Node, the text will go to the process’ standard output stream, rather than to a browser’s JavaScript console.

If you run node without giving it a file, it provides you with a prompt at which you can type JavaScript code and immediately see the result.

$ node
> 1 + 1
2
> [-1, -2, -3].map(Math.abs)
[1, 2, 3]
> process.exit(0)
$

The process variable, just like the console variable, is available globally in Node. It provides various ways to inspect and manipulate the current program. The exit method ends the process and can be given an exit status code, which tells the program that started node (in this case, the command-line shell) whether the program completed successfully (code zero) or encountered an error (any other code).

To find the command-line arguments given to your script, you can read process.argv , which is an array of strings. Note that it also includes the name of the node commands and your script name, so the actual arguments start at index 2. If showargv.js simply contains the statement console.log(process.argv) , you could run it like this:

$ node showargv.js one --and two
["node", "/home/marijn/showargv.js", "one", "--and", "two"]

All the standard JavaScript global variables, such as Array , Math , and JSON , are also present in Node’s environment. Browser-related functionality, such as document and alert , is absent.

The global scope object, which is called window in the browser, has the more sensible name global in Node.

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.