Javascript extending Inheritance

Question

I have 2 files below

transaction.js

class Transaction {
  constructor (txn) {
    this.txn = txn;
  }
  startTransaction () {
    this.conn.send(this.txn);
  }
}

index.js

const Transaction = require('./transaction')
class Index {
  constructor(option = {}) {
    this.conn = this.setConnection(option.url); // { url: '', send: [Function] }
    this.txn = Transaction;
  }
}
let index = new Index({url: ''})

I need to have index.conn object to be assigned under new index.transaction(), when newly instantiated. So that, code below would work

let transaction = new index.txn({ data: 'here' });
transaction.startTransaction();

Any possible way in your mind?

Answer 1

You can use Function.prototype.bind to pass the connection to the transaction:

transaction.js

class Transaction {
    constructor (conn, txn) {
        this.conn = conn;
        this.txn = txn;
    }
    startTransaction () {
        this.conn.send(this.txn);
    }
}

index.js

class Index {
    constructor(option = {}) {
        this.conn = this.setConnection(option.url); // { url: '', send: [Function] }
        this.txn = Transaction.bind({}, this.conn); /*
                                                       .bind() here will create a new function
                                                       that ensures this.conn will be passed as the
                                                       first argument to Transaction
                                                     */
    }
}

And run

let index = new Index({url: ''});
let transaction = new index.txn({ data: 'here' });
transaction.startTransaction();

Answer 2

Transaction.js

class Transaction {
  constructor (txn) {
    this.txn = txn;
  }
  startTransaction (conn) {
    conn.send(this.txn);
  }
}

Index.js

const Transaction = require('./transaction')
class Index {
  constructor(option = {}) {
    this.conn = this.setConnection(option.url); // { url: '', send: [Function] }
    this.txn = Transaction;
  }
  startTransaction (){
  this.txn.startTransaction(this.conn);
  }
}
let index = new Index({url: ''})

Then run

let index = new index.txn({ data: 'here' });
index.startTransaction();