Constructors in javascript

Question

how to declare parameterized constructors in JavaScript?? How it can be achieved in JavaScript??

 public class A()
 {
 //variable declaration
 public A()
 {
 //do something
 }
 public A(int a)
 {
 //do something
 }
 public A(int a,int b)
 {
 //do something
 }
 }

• madfriend: JavaScript is not Java. Period. You may have only one constructor, but choose different behaviors depending on arguments' types (e.g. typeof a == 'undefined')
• dumbass: This question is similar to: What techniques can be used to define a class in JavaScript, and what are their trade-offs?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.

Answer 1

JavaScript does not support overloading based on argument definitions.

Write a single function and check which arguments were received.

function A(a, b) {
 if (typeof a === "undefined") {
 // ...
 } else if (typeof b === "undefined") {
 // ...
 } else {
 // ...
 }
}

Answer 2

Any function in javascript can be a constructor

function A(paramA, paramB) {
 this.paramA = paramA;
 this.paramB = paramB;
 //do something
}
A.prototype.method1 = function(){
 console.log(this)
 console.log('Inside method 1' + this.paramA)
}
var a = new A(1, {name: 'Name'});
console.log(a.paramA);
console.log(a.paramB.name)
a.method1()

All instance variables can be created using this.<variable-name>=<value>;.
Instance methods can be created using the prototype property of the constructor function.

You can read more about constructors
Simple "Class" Instantiation
Simple JavaScript Inheritance

You also can check whether a parameter exists using

if(paramB == undefined) {
 //do something if paramB is not defined
}

• Grim: I think the 3rd line of code should be 'this.paramB = paramB' in order to work (can't make a 2 char edit to fix it though)

Answer 3

var Class = function(methods) { 
 var klass = function() { 
 this.initialize.apply(this, arguments); 
 }; 
 for (var property in methods) { 
 klass.prototype[property] = methods[property];
 }
 if (!klass.prototype.initialize) klass.prototype.initialize = function(){}; 
 return klass; 
};
var Person = Class({ 
 initialize: function(name, age) {
 this.name = name;
 this.age = age;
 },
 initialize: function(name, age, gender) {
 this.name = name;
 this.age = age;
 this.gender = gender;
 }
}); 
var alice = new Person('Alice', 26);
var rizwan = new Person('riz', 26, 'm');
alert(alice.name + ' - alice'); //displays "Alice"
alert(rizwan.age + ' - rizwan'); //displays "26"

http://jsfiddle.net/5NPpR/ http://www.htmlgoodies.com/html5/tutorials/create-an-object-oriented-javascript-class-constructor.html#fbid=OJ1MheBA5Xa