87 lines
2 KiB
Markdown
87 lines
2 KiB
Markdown
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---
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categories:
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- Programming Languages
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tags:
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- backend
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- node-js
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---
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# The `process` object in Node.js
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`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.
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For example, we can use it to get environment information, read environment variables, communicate with the terminal and exit the current process.
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## Managing runtime environments
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See [Managing Environments](/Programming_Languages/Node/Architecture/Managing_environments.md).
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## Accessing arguments: `process.argv`
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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.
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For instance if we run the following file:
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```js
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// process-demo.js
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console.log(3 + 3);
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console.log(process.argv);
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```
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We get:
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```bash
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6
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[
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'/Users/thomasbishop/.nvm/versions/node/v16.10.0/bin/node',
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'/Users/thomasbishop/prepos/testNode.js'
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]
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```
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The first value is a reference to the Node runtime binary. The second is the file that was passed to node.
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If we passed in a parameter we would get that too:
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```
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node process-demo.js --fakeFlag
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```
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Gives us:
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```bash
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[
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"/Users/thomasbishop/.nvm/versions/node/v16.10.0/bin/node",
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"/Users/thomasbishop/prepos/testNode.js",
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"--fake-flag",
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]
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```
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When writing command line Node applications we could easily write functions that parse standard input. For example:
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```js
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function parseStandardInput(flag) {
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let indexAfterFlag = process.argv.indexOf(flag);
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console.log(process.argv[indexAfterFlag]);
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}
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```
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Say we ran a program that took in a username:
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```bash
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node userName.js --user Thomas
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```
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Then `parseStandardInput("--user")` would give us `"thomas"`
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## Standard input and output `process.stdout`
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```js
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// alpha.js
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process.stdout.write("Hello from file \n");
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```
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```bash
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$ node alpha.js
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$ Hello from file
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```
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