What is spawn in Node JS ?

Node JS is a cross-platform, open-source back-end JavaScript runtime environment that uses the V8 engine to execute JavaScript code outside of an internet browser. In this article, we will learn about the Spawn in NodeJs.

Prerequisites

• NodeJS fundamentals
• Asynchronous Programming
• Child Processes

Spawn is a technique furnished by using the child_process module in Node.Js. It is used to spawn new approaches, allowing Node.Js programs to execute external instructions or different scripts as separate techniques. The spawn function creates a new baby manner asynchronously, offering admission to to the input/output streams for reading and writing information. This feature takes in the command to be carried out alongside an array of arguments and extra alternatives as parameters.

Syntax:

spawn(command[, args][, options])

The following is the description of the parameters used in the function:

• command: The command which is to be run.
• args: The list of string arguments that are to be passed to the process.
• options: The options object. It takes the following parameters:
  • cwd: The current working directory of the child process.
  • env: The environment key-value pairs. It has a default value of process.env.
  • argv0: The value of argument argv[0] sent to the child process. This will be set to command if not specified.
  • stdio: The child process’s stdio configuration.
  • detached: It is a boolean which tells whether the child is to be run independently of its parent process or not.
  • uid: The user identity of the process.
  • gid: The group identity of the process.
  • serialization: This specifies the kind of serialization used for sending messages between processes. It has a default value of ‘JSON’.
  • shell: It is a boolean that if true, runs the command inside of a shell.
  • timeout: It is the maximum amount of time the process is allowed to run. The value given should be in milliseconds.

Example 1: In this example, I am using spawn to run a child process that lists all the files and sub-directories in the current working directory.

Javascript

import { spawn } from "child_process";

const lsProcess = spawn("ls");
lsProcess.stdout.on("data", (data) => {
    console.log(`stdout:\n${data}`);
});
lsProcess.stderr.on("data", (data) => {
    console.log(`stdout: ${data}`);
});
lsProcess.on("exit", (code) => {
    console.log(`Process ended with ${code}`);
});

Output:

Example 2: In this example, I am running a python child process that prints the Hello World message on the stdout stream.

Javascript

import { spawn } from 'child_process';

const pythonProcess = spawn('python3', ['hello.py']);
pythonProcess.stdout.on('data', data => {
    console.log(`stdout:\n${data}`);
})
pythonProcess.stderr.on("data", (data) => {
    console.log(`stdout: ${data}`);
});
pythonProcess.on('exit', code => {
    console.log(`Process ended with ${code}`);
})

Output:

Reference: https://nodejs.org/api/child_process.html#child_processspawncommand-args-options