let’s assume we have installed node and npm.

First Node.js code. we will b writing very basic hello world program using Node.js. Follow the Following steps. 1. create one file and name it one.js. 2. write Following code console.log("Hello world"); 3. Goto the terminal and type node one.js.

you will see Following output.

  Hello world

Note: Node.js is a wrapper around v8 javascript engine written in C. Node.js provides a hosting environment for the V8 engine. For the systme input and output node uses process.

The upper code can be written as

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

will output the same.

for reading input from the command line process.argv.

for this reason we read sensitive data as process.env.data.

Node.js as command line util function

put the following in the file at the first line

#!/usr/bin/env node

then the file will become bash script.

e.g.

//1.js

#!/usr/bin/env node
console.log("Hey I will b working as a bash script");

Then make this file executable using chmode 700 1.js

./1.js
#output -----

Nature of Node.js function

Node.js has error first philosophy so, first argument of a program will be error variable.

var fs = require('fs');
content = fs.readfileSync('somefile.txt');
//Note all function in the module are `async` in nature

//Note:: if we do
console.log(content); // this will print Array Buffer to the screen.
//Make array buffer to print the file content do
console.log(content.toString()); // this will print our desired output.

//Async way
fs.readfile('somefile.txt',function(error, content){
  if(error){
    console.error(error);
    return; // exit(1)
  }else{
    console.log(content.toString()); //?? toString :: see above(read this code with the comments).
  }
});

Note all function in the module are async in nature if you want sync then use Sync with the functions.

Node REPL commands.

There are a few special REPL commands:

  • _ Will hold the value of the last output in the REPL. e.g. let arr = [1,2,3,34]; console.log(_);

  • .break - While inputting a multi-line expression, sometimes you get lost or just don’t care about completing it. .break will start over.
  • .clear - Resets the context object to an empty object and clears any multi-line expression.
  • .exit - Close the I/O stream, which will cause the REPL to exit.
  • .help - Show this list of special commands.
  • .save - Save the current REPL session to a file
  • .save ./file/to/save.js
  • .load - Load a file into the current REPL session.
  • .load ./file/to/load.js

Global variables in Node.js

  • __filename
  • __dirname
  • for more follow the link

Just for reference in ruby

  • __ FILE __
  • __ dir __
  • __ method __ _ __ callee __
  • __ LINE __

exports and module.exprots

exports.sayHelloInEnglish = function() {
  return "HELLO";
};

exports.sayHelloInSpanish = function() {
  return "Hola";
};

This can be written as


module.exports = {
  sayHelloInEnglish: function() {
    return "HELLO";
  },

  sayHelloInSpanish: function() {
    return "Hola";
  }
};

File streams in the Node.js

Here is the link for both file stream and pipe in Node.js i dint’ want to repeat follow the link

miscellaneous

  1. offline npm follow the link