Node.js

Core things in Node.js

proceses object

• In the process object, there is an argv property. Which gives us arguments, those we have passed via console.

  console.log(process.argv);
  

• We can pass any number of arguments as we want, and access it into the script.

  var index = process.argv.indexOf("Hello");
  console.log(process.argv[index]);
  

• We can also pass arguments as a flag.

  var index = process.argv.indexOf("--words") + 1;
  console.log(process.argv[index]);
  

• Write on the console using process object.

  process.stdout.write("Hello");
  process.stdout.write("World\n\n");
  

• Take input from console using process object.

  • But in this case program execution will never stop.
  • We have to stop it manually.

    process.stdin.on("data", (data) => {
    process.stdout.write(data);
    });
    

  

  • In below example stop manually process.

    process.stdin.on("data", (data) => {
    process.stdout.write(data);
    process.exit(); // this function call stop the process
    });
    

    

• Handle console logging inside the script.

  • In this example console will clear before each and every print statement.

    var index = 1;
    const interval = setInterval(() => {
    process.stdout.clearLine();
    process.stdout.cursorTo(0);
    process.stdout.write(${index++});
    }, 500);
    setTimeout(() => {
    clearInterval(interval);
    }, 3000);
    

    

util module

• Util module use for logging data on the console like console.log().
  • It displays data with time information.

    const util = require("util");
    util.log("Node.js process object");
    

    

v8 module

• Showing heap data of program execution.

  const v8 = require("v8");
  const util = require("util");
  util.log(v8.getHeapStatistics());
  

  

readline module

• readline has createInterface.

  • We have to provide read stream and output stream in the createInterface.

    const readline = require("readline");
    const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    });
    rl.question("Where are you living? ", (answer) => {
    rl.write(You are living in ${answer}\n);
    process.exit();
    });
    

    

events module

• event emtier allow us to create our own Event that we can call any time we want throughout the script's execution.

  const events = require("events");
  const emiter = new events.EventEmitter();
  emiter.on("customEvent", (message, sender) => {
  console.log("Inside the CustomEvent");
  console.log(${sender} sent you: ${message});
  });
  emiter.emit("customEvent", "Hii, there", "User");