Although I'm familiar with Object Oriented Programming (OOP) as I has been using Java for a long time, I've never tried to use it in JavaScript. When I researched OOP in JavaScript, I found it a little complicated because there exist a few ways to implemnt. In this article, I sorted out and simplified them.
- Use function as class cannot be used in JavaScript before ES5.
var ES5Class = (function() { // constructor var ES5Class = function(member) { // Cope with the following usage which doesn't use new operator. // var instance = ES5Class(); if(!(this instanceof ES5Class)) { return new ES5Class(member); } // members // Conventionally prefix an under score to the name of private variables. // (Although it can be accessed from outside the class.) this._member = member; }; // Declare a method with prototype. // Methods can be declared in following way, but it's not efficient // because functions will be created every time an instance is generated. // this.printMethod = function... var p = ES5Class.prototype; // methods p.printMember = function () { console.log(this._member); } return ES5Class; })(); module.exports = ES5Class;
- With JavaScript later than ES6, class syntax can be used to declare classes.
class ES6Class { // constructor constructor(member) { // memners // Conventionally prefix an under score to the name of private variables. // (Although it can be accessed from outside the class.) this._member = member; } printMember() { console.log(this._member); } } module.exports = ES6Class
- class syntax can also define static methods but cannot define static members.
// As there is no way to declare static members in class syntax, // define global-scope variables instead. var _member = 0; class ES6StaticClass { // static methods static printMember() { _member++; console.log(_member); } } module.exports = ES6StaticClass
