Create many instances with module pattern

Question

I have two files:

let WordPair = function(wordA, wordB) {
  function doSomething() { ... };

  const smth = wordA + wordB;
  return {doSomething, smth};
};
module.exports = WordPair;

-

let wordpair = require('./WordPair.js')('dog', 'cat');
wordpair.doSomething();

Now that works fine, but what I want to do is creating many instances of WordPair, for example like this:

let arr = [];
for (let i = 0; i < 10; i++) {
  arr.push(new WordPair('xyz', 'abc'));
}

In other words: How you would use instances of a class in Java. What's the correct way to achieve this in Javascript?

Ken Yip · Accepted Answer · 2019-03-05 03:03:53Z

1

in javascript, you can use prototype pattern to achieve that

suppose doSomething is class method that combine the wordA and wordB

function WordPair(wordA, wordB){
    this.wordA = wordA;
    this.wordB = wordB;
}

WordPair.prototype.doSomething = function(){
    const something = this.wordA + this.wordB;
    console.log(something);
}

const wordPair = new WordPair('xyz', 'abc');

wordPair.doSomething();

or more es6 class way

class WordPair {

    constructor(wordA, wordB){
        this.wordA = wordA;
        this.wordB = wordB;
    }

    doSomething(){
        const something = this.wordA + this.wordB;
        console.log(something);
    }

}

const wordPair = new WordPair('xyz', 'abc');

wordPair.doSomething();

answered Mar 5, 2019 at 3:03

Ken Yip

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5 Comments

Vu Luu Over a year ago

that's right. JavaScript classes, introduced in ECMAScript 2015, are primarily syntactical sugar over JavaScript's existing prototype-based inheritance. The class syntax does not introduce a new object-oriented inheritance model to JavaScript.

gnidoc Over a year ago

So there is no way doing what I want using the Reveiling Module Pattern as I tried, I have to manipulate the prototype?

gnidoc Over a year ago

What If in your first example I want to avoid "this" to keep the variables encapsuled/private? I tried to adapt your example but didn't get it to work. wordA = 'xyz' instead of this.wordA = [...] and in doSomething() replace this.wordA by wordA. I get an error "wordA is not defined".

Ken Yip Over a year ago

You can create a get method for wordA and wordB to keep them as private. function WordPair(wordA, wordB){ this.getWordA = function(){ return wordA; } this.getWordB = function(){ return wordB; } } WordPair.prototype.doSomething = function(){ const something = this.getWordA() + this.getWordB(); console.log(something); }

gnidoc Over a year ago

Why is it not possible to add the getter-functions to the prototype just as you did with "doSomething"? This prints 'undefined':

function WordPair(_wordA){ let wordA = _wordA;} WordPair.prototype.getWordA = function(){ return this.wordA; } const wordPair = new WordPair('xyz'); console.log(wordPair.getWordA());

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