eolas/Programming_Languages/Node/Architecture/Process_object.md

categories	tags
Programming Languages	backend node-js

The process object in Node.js

process is a global object accessible from anywhere in a Node application. It contains functionality that allows us to interact with information about the current process instance.

For example, we can use it to get environment information, read environment variables, communicate with the terminal and exit the current process.

Managing runtime environments

See Managing Environments.

Accessing arguments: process.argv

We can use process.argv to return an array containing the command-line arguments passed when a Node process was launched. This could be a whole-app entrypoint (i.e. index.js) or a single file we are running.

For instance if we run the following file:

// process-demo.js
console.log(3 + 3);
console.log(process.argv);

We get:

6
[
  '/Users/thomasbishop/.nvm/versions/node/v16.10.0/bin/node',
  '/Users/thomasbishop/prepos/testNode.js'
]

The first value is a reference to the Node runtime binary. The second is the file that was passed to node.

If we passed in a parameter we would get that too:

node process-demo.js --fakeFlag

Gives us:

[
  "/Users/thomasbishop/.nvm/versions/node/v16.10.0/bin/node",
  "/Users/thomasbishop/prepos/testNode.js",
  "--fake-flag",
]

When writing command line Node applications we could easily write functions that parse standard input. For example:

function parseStandardInput(flag) {
  let indexAfterFlag = process.argv.indexOf(flag);
  console.log(process.argv[indexAfterFlag]);
}

Say we ran a program that took in a username:

node userName.js --user Thomas

Then parseStandardInput("--user") would give us "thomas"

Standard input and output process.stdout

// alpha.js
process.stdout.write("Hello from file \n");

$ node alpha.js
$ Hello from file