devarajchidambaram

Difference between spawn and exec functions of child_process

The Node.js Child Processes module (child_process) has two functions spawn and exec, using which we can start a child process to execute other programs on the system. Those new to child_process may wonder why there are two functions to do the same thing, and which one they should use. I'll explain the differences between spawn and exec to help you decide when to use what.

The most significant difference between child_process.spawn and child_process.exec is in what they return - spawn returns a stream and exec returns a buffer.

child_process.spawn returns an object with stdout and stderr streams. You can tap on the stdout stream to read data that the child process sends back to Node. stdout being a stream has the "data", "end", and other events that streams have. spawn is best used to when you want the child process to return a large amount of data to Node - image processing, reading binary data etc.

child_process.spawn is "asynchronously asynchr

devarajchidambaram

/*
USE OF MUTIPLE THEN IN THE PROMISES

Actually in then we can return a sync value or 
multiple async values

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then#Chaining
**/

var p1 = new Promise(function (resolve, reject) {

devarajchidambaram

const express = require('express');
const path = require('path');
const bodyParser = require('body-parser');
const session = require('express-session');
const cors = require('cors');
const mongoose = require('mongoose');
const errorHandler = require('errorhandler');

//Configure mongoose's promise to global promise
mongoose.promise = global.Promise;

devarajchidambaram

const express = require('express');
const path = require('path');
const bodyParser = require('body-parser');
const session = require('express-session');
const cors = require('cors');
const mongoose = require('mongoose');
const errorHandler = require('errorhandler');

//Configure mongoose's promise to global promise
mongoose.promise = global.Promise;

devarajchidambaram

const EventEmitter = require('events');
const myEmitter = new EventEmitter();
myEmitter.on('fire', ()=>console.log('fire1'))
myEmitter.on('fire',  ()=>console.log('fire2'))
myEmitter.on('fire',  ()=>console.log('fire3'))

myEmitter.prependListener('fire',  ()=>console.log('fire tooppppp'))
myEmitter.emit('fire')
          

devarajchidambaram

var path = require('path')
var fs = require('fs');

function getNpmVersion(npmName) {

    try {
        var npmPath = require.resolve(npmName)
        var npmDirName = path.dirname(npmPath)
        return JSON.parse(fs.readFileSync(path.join(npmDirName, '/package.json'))).version;
    } catch (e) {

devarajchidambaram

var fs = require('fs');
var profiler = require('@risingstack/v8-profiler')
var request = require('request')
var samplingIntervalMicros = 1000;
var express = require('express')
var app = express();
var bodyParser = require('body-parser')

var enableProfiler = false;

devarajchidambaram

NODE_ENV works like any other environment variable (e.g. PATH) and it depends on your platform how to set it:

Linux and OSX: export NODE_ENV=production
Windows: SET NODE_ENV=production

In nodejs app we can get it 

process.env.NODE_ENV

devarajchidambaram

//Referred link https://www.lunchbadger.com/tracking-the-performance-of-express-js-routes-and-middleware/
var express = require('express')
var uuid = require('uuid')

const bodyParser = require('body-parser');
const {
    EventEmitter
} = require('events');
const profiles = new EventEmitter();

devarajchidambaram

function myFunc(arg) {
  console.log(`arg was => ${arg}`);
}
//In nodejs we can pass the arguments..
// nodejs,  actually provides its own implementation of these timer methods
setTimeout(myFunc, 1500, 'funky');

//> clear
//clearImmediate  clearInterval   clearTimeout