undefined return from a class instance - Java Script

Question

I just asked this question and i thought it was resolved but it isnt.. so here it is again.. apologies for the double post..

I have a file: block.js:

class Block{
    constructor(timeStamp, lastBlockHash, thisBlockData, thisBlockHash){
        this.timeStamp = timeStamp;
        this.lastBlockHash = lastBlockHash;
        this.thisBlockData = thisBlockData; 
        this.thisBlockHash = thisBlockHash;
        }

    static genesis(){
        return new Block(Date.now(), "---", "This is the genesis block", "hash of the genesis");
    }
}

another file: blockchain.js:

const Block = require('./block');

class BlockChain{
    constructor() {
        this.chain = Block.genesis();
    }
}

module.exports = {BlockChain};

and finally a test file test.js:

const BlockChain = require("./blockchain.js");
let blockChainInstance = new BlockChain();

console.log(blockChainInstance.chain);

the output of the test.js file is showing "undefined" in place of a genesis block.. this has been a mystery for me since morning.. and i would be immensely grateful if anyone can solve this for me..

Cheers, al

Petr Broz · Accepted Answer · 2018-09-18 13:45:10Z

2

Not sure if that's the root cause of your issue, but in blockchain.js you're basically exporting the class as

module.exports = {
    BlockChain: BlockChain
};

And so, in test.js you should import the class using

const { BlockChain } = require('./blockchain.js');

answered Sep 18, 2018 at 13:45

Petr Broz

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1 Comment

thealchemist Over a year ago

i am not able to reproduce the error i had since morning.. i didnt edit anything but somehow i am not getting the same error.. if anyone is able to reproduce my original error please comment so we can have a chat.. :) cheers.. thanks Petr and everyone who spent some time

Petr Broz · Accepted Answer · 2018-09-18 13:47:19Z

0

You have to export the Block class:

  module.exports = class Block { /*...*/ };

same for the BlockChain class.

edited Sep 18, 2018 at 13:47

Petr Broz

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answered Sep 18, 2018 at 13:44

Jonas Wilms

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