Node.js os.constants

The os.constants is an inbuilt application programming interface of the os module which is used to get operating system specified constants for error code, signal constants, priority constants, dlopen constants, etc.

Syntax:  

os.constants

Return Value: It returns an object that contains operating system-specified constants. 

Examples: error codes, signal constants, priority constants, dlopen constants, etc.

Signal constants can be accessed by using os.constants.signals and priority constants can be accessed by using os.constants.priority. 

Some of the constants are listed below:

Signal Constants: 

Error constants: 

1. POSIX error constant 
 

2. Windows specific error 
 

dlopen Constants: 
 

Priority constants: 
 

libuv Constants: 
 

The below examples illustrate the use of os.constants in Node.js:

Example 1: 

// Import os module
const os = require('os');

constants = os.constants;

// Printing all os.constants
console.log(constants);

Output: 

[Object: null prototype] {
  UV_UDP_REUSEADDR: 4,
  dlopen: [Object: null prototype] {},
  errno:
   [Object: null prototype] {
     E2BIG: 7,
     EACCES: 13,
     EADDRINUSE: 100,
     . . .
     PRIORITY_HIGH: -14,
     PRIORITY_HIGHEST: -20 } }

Example 2: 

// Import os module
const os = require('os');

constants = os.constants;

// Printing os.constants

// Signals constants
if(constants.signals != undefined){
    console.log("Signals:");
    console.log(constants.signals);
}

// Priority constants
if(constants.priority!=undefined){
    console.log("priority:");
    console.log(constants.priority);
}

Output: 

Signals:
[Object: null prototype] {
  SIGHUP: 1,
  SIGINT: 2,
  . . .
  PRIORITY_HIGH: -14,
  PRIORITY_HIGHEST: -20 }

Note: The above program will compile and run by using the node index.js command.

Reference: https://nodejs.org/api/os.html#os_os_constants