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NodeJS I


1. Install


       Download from https://nodejs.org/en/

2.Verify 

        Open the CMD and type: node -v   or type   npm -v

        If in the screen appear the node version, the installation has been done with success


First Example

var rect = {
perimeter: function (x, y) {
           return (2*(x+y));
},
area: function (x, y) {
            return (x*y);
}
};

function solveRect(l,b) {
    console.log("Solving for rectangle with l = " + l + " and b = " + b);

    if (l < 0 || b < 0) {
        console.log("Rectangle dimensions should be greater than zero:  l = "
               + l + ",  and b = " + b);
    }
    else {
console.log("The area of a rectangle of dimensions length = "
               + l + " and breadth = " + b + " is " + rect.area(l,b));
console.log("The perimeter of a rectangle of dimensions length = "
               + l + " and breadth = " + b + " is " + rect.perimeter(l,b));
    }
}

solveRect(2,4);
solveRect(3,5);
solveRect(-3,5);


Execute 

Type node <File name>



Two main features

  • A function can be treated as any other variable
  • Closure
    • An inner function can access to all the variables declared in the outside function
    • The access will continue after the outer function has return

Node Modules

Javascript doesn't define any standart library as C or C++

CommonJS API is a JavaScript standart library, it define APIs for common aplication needs
  • Defines a module format
  • NodeJS follows the CommonJS module specification

Node Modules

  • Each file is a Node module
  • module variable give access to the current module definition in a file
  • module.exports variable determines the export from the current module
  • require function is used to import a module


module.exports = {
perimeter: function(x,y){ return(2*(x+y));
},
area: function(x,y){return ( x);
}
};

You can write the same using:  exports
exports = module.exports

exports.perimeter =  function(x,y){ 
      return(2*(x+y));
}
exports.area =  function(x,y){
return(x*y);
}


The file is import using 

var rect = require('./rectangle');


var rect = require('./rectangle-1');

function solveRect(l,b) {
    console.log("Solving for rectangle with l = " + l + " and b = " + b);

    if (l < 0 || b < 0) {
        console.log("Rectangle dimensions should be greater than zero:  l = "
               + l + ",  and b = " + b);
    }
    else {
console.log("The area of a rectangle of dimensions length = "
               + l + " and breadth = " + b + " is " + rect.area(l,b));
console.log("The perimeter of a rectangle of dimensions length = "
               + l + " and breadth = " + b + " is " + rect.perimeter(l,b));
    }
}

solveRect(2,4);
solveRect(3,5);
solveRect(-3,5);



Execute 
Type:  node solve-1

Node Modules

  • File-based Modules
  • Core Modules
    • Part of core Node (Ej, path, fs, util, .....)
  • External Modules
    • Third-party modules
    • This modules are installed in node_modules

Use of Modules

  • File-based Modules
    • require('./<module_name>')
  • External Modules
    • require('<module_name>')
    • looks for in: ./modules

Install

  • npm install express@4.0.0
  • Patch acceptable version :  npm install express@"~4.0.0"
  • Minor acceptable version :  npm install express@"ˆ4.0.0"

  • Example:  npm install yargs --save
  • --save:  save dependencies in our package.json file

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