[[oktatas:web:nodejs|< Node.js]]

====== Node.js modul ======

  * **Szerző:** Sallai András
  * Copyright (c) 2021, Sallai András
  * Licenc: [[https://creativecommons.org/licenses/by-sa/4.0/|CC Attribution-Share Alike 4.0 International]]
  * Web: https://szit.hu

===== Modulkészítés =====

==== Érték exportálása ====

<code javascript pi.js>
module.exports = 3.14
</code>

<code javascript app.js>
const pi = require('./pi.js');
console.log(pi)
</code>

==== Függvények objektumon keresztül ====

Két függvényt a triangle objektumon keresztül érünk el:

<code javascript triangle.js>
module.exports = {
	calcPerimeter: function (sidea, sideb, sidec) {
		return sidea + sideb + sidec;
	},
	calcArea: function (base, height) {
		return base*height/2;
	}
}
</code>


<code javascript app.js>
const triangle = require('./triangle.js');

console.log(triangle.calcPerimeter(30, 35, 40));
console.log(triangle.calcArea(30, 35));
</code>

A triangle objektum. De kinyerhetem belőle a két függvényt:
<code javascript app.js>
const triangle = require('./triangle.js');
const calcPerimeter = triangle.calcPerimeter;
const calcArea = triangle.calcArea;

console.log(triangle.calcPerimeter(30, 35, 40));
console.log(triangle.calcArea(30, 35));


console.log(typeof(calcArea));
</code>

==== Függvény exportálása ====

<code javascript rectangleArea.js>
module.exports = function(base, height) {
  return base*height;
}
</code>


<code javascript app.js>
const rectangleArea = require('./rectangleArea.js');
console.log(rectangleArea(30, 35));
</code>

==== Objektum exportálása ====

<code javascript employees.js>
module.exports =  [
    { name: 'Nagy János', city: 'Hatvan' },
    { name: 'Kis Irén', city: 'Szolnok'}
  ];

</code>


<code javascript app.js>
const employees = require('./employees.js');
console.log(employees[0].name);
</code>

===== Helyi változók =====

<code javascript triangle.js>
let maxSize = 100;

module.exports = {
	calcPerimeter: function (sidea, sideb, sidec) {
		if (	sidea < maxSize &&
			  	sideb < maxSize  &&
			  	sidec < maxSize)
				return sidea + sideb + sidec;
		else
				console.log("Error! Side is too large!");
	},
	calcArea: function (base, height) {
		if (base < maxSize && height < maxSize)
				return base*height/2;
		else
				console.log("Error! Side is too large!");
	}
}

</code>

===== Osztály =====

<code javascript Employee.js>
module.exports = class Employee {
    constructor(name, city) {
      this.name = name || 'Névtelen';
      this.city = city || 'Ismeretlen';
    }
}
</code>


<code javascript app.js>
const Employee = require('./employee.js');

const janos = new Employee('Nagy János', 'Szolnok');
console.log(janos.name);

console.log(typeof(Employee));
console.log(typeof(janos));
</code>

Az Employee függvényként jelenik meg, de a janos már objektumoként.


===== Források =====

  * https://www.hacksparrow.com/nodejs/writing-modules.html (2021)
  * https://initialcommit.com/blog/nodejs-module (2021)
  * https://docs.npmjs.com/creating-node-js-modules (2021)
  * https://www.digitalocean.com/community/tutorials/how-to-create-a-node-js-module (2021)