JavaScript pattern for multiple constructors

Question

I need different constructors for my instances. What is a common pattern for that?

Answer 1

you can use class with static methods that return an instance of that class

    class MyClass {
        constructor(a,b,c,d){
            this.a = a
            this.b = b
            this.c = c
            this.d = d
        }
        static BAndCInstance(b,c){
            return new MyClass(null,b,c)
        }
        static BAndDInstance(b,d){
            return new MyClass(null,b, null,d)
        }
    }

    //new Instance just with a and other is nul this can
    //use for other params that are first in constructor
    const myclass=new MyClass(a)

    //an Instance that has b and c params
    const instanceWithBAndC = MyClass.BAndCInstance(b,c)

    //another example for b and d
    const instanceWithBAndD = MyClass.BAndDInstance(b,d)

with this pattern you can create multi constructor

Answer 2

Sometimes, default values for parameters is enough for multiple constructors. And when that doesn't suffice, I try to wrap most of the constructor functionality into an init(other-params) function that is called afterwards. Also consider using the factory concept to make an object that can effectively create the other objects you want.

http://en.wikipedia.org/w/index.php?title=Factory_method_pattern&oldid=363482142#Javascript

Answer 3

This is the example given for multiple constructors in Programming in HTML5 with JavaScript and CSS3 - Exam Ref.

function Book() {
    //just creates an empty book.
}


function Book(title, length, author) {
    this.title = title;
    this.Length = length;
    this.author = author;
}

Book.prototype = {
    ISBN: "",
    Length: -1,
    genre: "",
    covering: "",
    author: "",
    currentPage: 0,
    title: "",

    flipTo: function FlipToAPage(pNum) {
        this.currentPage = pNum;
    },

    turnPageForward: function turnForward() {
        this.flipTo(this.currentPage++);
    },

    turnPageBackward: function turnBackward() {
        this.flipTo(this.currentPage--);
    }
};

var books = new Array(new Book(), new Book("First Edition", 350, "Random"));