The javascript function is returning a promise and the promise is used in the solidity function which gives the error of invalid arguments

I am trying to make a Dapp which maintains the various versions of a trade(new versions are created when we update the data of trade). I am using javascript we3.js api to call my solidity functions through javascript. I have a function which displays the data when we search using a field called 'client'. When I am clicking the button to search on basis of client, it returns an error. I am using promises in javascript, but it seems to me that the javascript function is returning a promise which is undefined to solidity function. But after the error the javascript function is returning the expected values(I checked using console.log).

I am trying to make a Dapp which maintains the various versions of a trade(new versions are created when we update the data of trade). I am using javascript we3.js api to call my solidity functions through javascript. I have a function which displays the data when we search using a field called 'client'. When I am clicking the button to search on basis of client, it returns an error. I am using promises in javascript, but it seems to me that the javascript function is returning a promise which is undefined to solidity function. But after the error the javascript function is returning the expected values(I checked using console.log).

I have tried using async/await but that doesnt seems to do the trick.

My Javascript code:-

getVersion:async function(i){

var returnedLatestVersion;

App.contracts.Trades.deployed().then(async function(instance){

await instance.getLatestVersionOfTrade.call(i).then(function(a){      

  returnedLatestVersion = a;
  console.log("test:"+returnedLatestVersion+",a:"+a);

}).catch(function(err){
console.log(err)
})
console.log("test2="+returnedLatestVersion);
return await returnedLatestVersion;    

})
},

searchByClient: function(){

var tradesInstance;

var client = $('#clientSearch').val();

var tradeResults = $("#tradesResult");
tradeResults.empty();

App.contracts.Trades.deployed().then(function(instance){
tradesInstance = instance;

return tradesInstance.getClientData.call(client).then(async function(returnValues){

console.log("returnValues Array = "+returnValues);

var returnValuesLength = returnValues.length;   

for(var i=0;i<returnValuesLength;i++){     

  var a = returnValues[i];
  var c = returnValues[i];    
  var j;

  j = await App.getVersion(a);

  console.log("version ="+j);
  console.log("tradeId="+a);

  tradesInstance.trades(c,j).then(function(trade){

    var secId = trade[0];
    var notional = trade [1];
    var price = trade[2];
    var client = trade[3];

    var tradeTemplate = "<tr><td>" + secId + "</td><td>" + notional + "</td><td>" + price + "</td><td>" + client +"</td></tr>" 
    tradeResults.append(tradeTemplate);
  })
}

}).catch(function(err){
console.log(err);
})
}).catch(function(err){
console.warn(err);
})

}

};

My Smart Contract :-

pragma solidity 0.5.0;

contract Trades {
struct Trade {
string secId;
uint notional;
uint price;
string client;
uint version;
uint index;
uint tradeId;
}

mapping(uint =>mapping(uint => Trade)) public trades;

uint public tradeId;
uint[] tradeIndex;
uint[] tradeID;
uint[] public totalNum;

function updateTrade(uint _tradeId, string memory _secId,uint _notional,uint _price,string memory _client) public{

uint j;
j= (getLatestVersionOfTrade(_tradeId)) + 1;
trades[_tradeId][j].secId = _secId;
trades[_tradeId][j].notional = _notional;
trades[_tradeId][j].price = _price;
trades[_tradeId][j].client = _client;
trades[_tradeId][j].version = j;
trades[_tradeId][j].index = tradeIndex.push(tradeIndex[tradeIndex.length-1]+1);

}

function setTrade(string memory _secId,uint _notional,uint _price,string memory _client) public {

uint  version  = 0;
tradeId++;

trades[tradeId][version].secId = _secId;
trades[tradeId][version].notional = _notional;
trades[tradeId][version].price = _price;
trades[tradeId][version].client = _client;
trades[tradeId][version].version = version;
trades[tradeId][version].index = tradeIndex.push(tradeId);
tradeID.push(tradeId);

}

function getAllTradeData()view public returns(uint[] memory){
return tradeIndex;
}

function getAllTradeDataId()view public returns(uint[] memory){
return tradeID;
}

function getTradeById(uint _tradeId,uint version)view public returns(string memory, uint, uint, string memory, uint, uint){
return (trades[_tradeId][version].secId, trades[_tradeId][version].notional, trades[_tradeId][version].price,
trades[_tradeId][version].client,trades[_tradeId][version].version, trades[_tradeId][version].index);
}

function getLatestVersionOfTrade(uint _tradeId) view public returns (uint) {
uint max = 0;

for (uint i = 0; i < tradeIndex.length; i++) {
    uint ver = trades[_tradeId][i].version;
    if (ver > max) {
        max = ver;
    }
}

return max;
}

function getClientData(string memory _client) public returns (uint[] memory) {

if (totalNum.length > 0){
    delete totalNum;
}
    for(uint i=1; i <= tradeID.length;i++){
    uint j;
    j= (getLatestVersionOfTrade(i));
    if(uint(keccak256(abi.encodePacked(trades[i][j].client))) == uint(keccak256(abi.encodePacked(_client)))){
        totalNum.push(i);
    }             
}  
return totalNum;

}

function getTotalNumLength() public returns (uint){
return totalNum.length;
}
}

The error shown on brower console : -

returnValues Array = 3,4,5
app.js:113 version =undefined
app.js:114 tradeId=3
app.js:113 version =undefined
app.js:114 tradeId=4
app.js:113 version =undefined
app.js:114 tradeId=5

3inpage.js:1 Uncaught (in promise) Error: Invalid number of arguments to
Solidity function
at Object.InvalidNumberOfSolidityArgs (inpage.js:1)
at u.validateArgs (inpage.js:1)
at u.toPayload (inpage.js:1)
at u.call (inpage.js:1)
at u.execute (inpage.js:1)
at truffle-contract.js:136
at new Promise (<anonymous>)
at truffle-contract.js:127

app.js:77 test:0,a:0
app.js:82 test2=0
app.js:77 test:0,a:0
app.js:82 test2=0
app.js:77 test:1,a:1
app.js:82 test2=1

The variable 'j' in searchByClient is returning an undefined value when it is passed in 'trades(c,j)'. But in the function getVersion the value returning seems to be fine. Please help me out as I have no other options left. Also I am extremly new to javascript, so please do tell me if I had make any mistakes. I was able to write this code with help of a tutorial.

How to Build a Blockchain in JavaScript

How to Build a Blockchain in JavaScript

For the purpose of this blog, let’s build a blockchain written in JavaScript. Hopefully, this doesn’t just serve as a simple code example but also gives a very basic understanding of how a blockchain actually works.

Blockchain is all the buzz now. And for good reason! A distributed public ledger that is extremely secure through encryption?! Imagine the millions of applicable use cases. A blockchain can be created and maintained using any modern language.

For the purpose of this blog, let’s dive into a blockchain written in JavaScript. Hopefully, this doesn’t just serve as a simple code example but also gives a very basic understanding of how a blockchain actually works.

Creating A Block

Let’s first create a block and give it some attributes.

  • BlockIndex – the position of the block on the blockchain.
  • BlockCreatedWhen – when the block was created.
  • BlockTransaction – a type of data to be stored on the block. This could be any exchange of value really. Perhaps an array of sorts.
  • BlockPreviousHash – hash of the previous block. This ties one block to another.
  • Hash – calculated hash function using the properties of the block. This is the block identifier on the blockchain. There is currently no built-in functionality for hash functions outside of the WebCryptoAPI. But there are plenty of other external libraries such as object-hash, crypto-hs, SJCL, forge SHA-256, etc.
  • Nonce – Proof of work
  • Merkle Root – A Merkle Root hash that houses all hashed transactions tied to a particular block.
const hash = require('crypto-js/sha256'); // could also use object-hash, Stanford Javascript Crypto Library (SJCL), forge SHA-256, jsSHA, etc
 
class VincentsBlock{
         
    constructor(blockIndex, blockCreatedWhen, blockTransactions, blockPreviousHash) {
        this.blockIndex = blockIndex;
        this.blockCreatedWhen = blockCreatedWhen;
        this.blockTransactions = blockTransactions;  // an array of transactions
        this.blockPreviousHash = blockPreviousHash;
        this.hash = this.calculateBlockHash();
        this.nonce = 0;  // needed for proof of work
        this.merkleRoot = this.computeMerkleRoot()  // used to validate transactions within block
    } 
 
    calculateBlockHash() { 
        return hash(this.blockIndex + JSON.stringify(this.blockTransaction) + this.blockPreviousHash + this.blockCreatedWhen + this.nonce + this.merkleTreeRoot).toString();
    }
     
    computeMerkleRoot() {
        let treeList = this.generateMerkleTreeRoot();
         
        return treeList[treeList.length-1];
    }
 
    generateMerkleTreeRoot() {
        let tree = [];
        let transactionCount = this.blockTransactions.length;
 
        for (var i=0; i<transactionCount; i++) { tree.push(this.blockTransactions[i].hash); } let levelOffset = 0; for (let levelSize = transactionCount; levelSize > 1; levelSize = (levelSize + 1) / 2) {          
            for (let left = 0; left < levelSize; left += 2) {            
                let right = Math.min(left + 1, levelSize - 1);
                let tleft = tree[levelOffset + left];
                let tright = tree[levelOffset + right];
                tree.push(hash(tleft + tright));
            }            
            levelOffset += levelSize;
        }
 
        return tree;
    }
}
 
module.exports = VincentsBlock;

Notice the Merkle Root property on the block. Given that a transaction has its own hash generated, we can create a Merkle Tree out of the transaction list. This tree can then be used to validate the block transactions. Now that a block is generated, let’s go back and look at a transaction object. This should illustrate that a transaction can be anything really. This is where the many applications of blockchain come into play.

These particular transactions consist of a

  • transactionId (id of transaction),
  • inputAccount (sender),
  • outputAccount (receiver),
  • fee (perhaps in BTC or any other currency),
  • the amount (processed amount),
  • type,
  • misc (notes)
  • timestamp (timestamp of transaction)
  • hash (hash of transaction)

Creating a Block Transaction Object

I created a block transaction object as follows:

const hash = require('crypto-js/sha256');
 
class VincentsTransaction{
         
    constructor(transactionId, inputAccount, outputAccount, fee, amount, type, misc, timestamp) {
        this.transactionId = transactionId,   // could be hex address
        this.inputAccount = inputAccount;    // sender
        this.outputAccount = outputAccount;   // receiver
        this.fee = fee;    // fee of transaction
        this.amount = amount;    // amount of transaction processed
        this.type = type;      // type of transaction
        this.misc = misc;     // misc note text
        this.timestamp = timestamp    // timestamp of block
        this.hash = this.calculateTransactionHash();  // hash of the transaction
    } 
 
    calculateTransactionHash() { 
        return hash(this.transactionId + this.inputAccount + this.outputAccount + this.fee + this.amount + this.type + this.misc + this.timestamp).toString();
    }
}
 
module.exports = VincentsTransaction;
The Chain

Moving on to the good part, let’s take a look at a basic immutable blockchain using the above blocks.

Below, in the constructor, you will notice a manual creation of the first block. This is needed to get the ball rolling. Every chain needs a first link!

Let’s manually create it and give it an index of 0 to show its placement on the chain. Many functions can be added to this class to assist on tasks such as adding blocks, checking for an empty chain, grabbing the latest block, validation, etc.

The process of creating additional blocks can be a complex one involving tons of validation if needed. We must keep in mind to regenerate the hash if any other property changes on a block.

In regards to validation of the blockchain, for now, we will focus on blocks linked together. Since index 0 corresponds to the manually created first block, we can skip it and check the hash of corresponding linked blocks.

let VincentsBlock = require('./VincentsBlock');
 
class VincentsBlockChain {
     
    constructor() {
        this.chain = [this.createBrandNewBlock()];
 
        //this.current_transactions = [];
    }
 
    createBrandNewBlock() {
        return new VincentsBlock(0, "01/01/2019", "Initial Block", ""); //no hash needed here since this is a manual creation of the first block.
    }
 
    createAdditionalBlock(newBlock) {
        ///very simplistic... could have more validation in place here.  
        let previousBlock = this.getLatestBlock();
        newBlock.index = previousBlock.index + 1; 
        newBlock.blockPreviousHash = this.getLatestBlock().hash;
        newBlock.hash = newBlock.calculateBlockHash(); //need to regenerate hash if any properties in our block changes
        this.chain.push(newBlock);
    }
 
    getLatestBlock() {
        return this.chain.slice(-1)[0];        
    }
 
    isEmpty() {
        return this.chain.length == 0;
    } 
 
    isBlockChainValid() { 
        for(let i = 1;i < this.chain.length; i++) {
            const currentBlock = this.chain[i];
            const previousBlock = this.chain[i - 1];
 
            if (currentBlock.blockPreviousHash != previousBlock.hash) { // does our block match up to correct previous hash property? 
                return false;
            }            
 
            if (currentBlock.hash != currentBlock.calculateBlockHash()) { // does the actual hash of the block match up to it's current hash property?
                return false;
            }     
              
            if (previousBlock.index + 1 !== currentBlock.index) { // do the indexes line up in order?
                return false;
            }  
        }
 
        return true;
    }
};
 
module.exports = VincentsBlockChain;
Adding to the Chain

For this simplistic example, let’s create 10 blocks, each with multiple transactions, and add them to the chain.

let VincentsBlockChain = require( "./blockchain/VincentsBlockChain");
let VincentsBlock = require( "./blockchain/VincentsBlock");
let VincentsTransaction = require( "./blockchain/VincentsTransaction");
 
let blockChain = new VincentsBlockChain();
blockChain.createAdditionalBlock(new VincentsBlock(1, "01/02/2019", [new VincentsTransaction(123, "abcxyz", "xyzabc", 30, "btc"), new VincentsTransaction(999, "uyyuyy", "xxdzkj", 550, "btc"), new VincentsTransaction(653, "drerea", "kioolk", 70, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(2, "01/03/2019", [new VincentsTransaction(234, "sfgfsd", "rrttyu", 50, "eth"), new VincentsTransaction(555, "iuiuii", "rrttyu", 50, "eth"), new VincentsTransaction(553, "hghghg", "ffgfff", 80, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(3, "01/04/2019", [new VincentsTransaction(345, "srthhf", "oouyuu", 65, "btc"), new VincentsTransaction(452, "jhghgg", "rrttyu", 11, "eth"), new VincentsTransaction(230, "wewfgf", "ghjgtt", 230, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(4, "01/05/2019", [new VincentsTransaction(456, "sfgfss", "xzsdee", 4, "btc"), new VincentsTransaction(780, "fgtfdd", "rrttyu", 22, "eth"), new VincentsTransaction(112, "qwewue", "hgyuyu", 280, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(5, "01/06/2019", [new VincentsTransaction(567, "xxcbbf", "nbvbcx", 545, "eth"), new VincentsTransaction(677, "fdfsaa", "uytttt", 33, "eth"), new VincentsTransaction(111, "hjhjh", "huiuii", 5480, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(6, "01/07/2019", [new VincentsTransaction(678, "uiyuyy", "dfgree", 5, "btc"), new VincentsTransaction(553, "ooouio", "yuyuuu", 55, "eth"), new VincentsTransaction(467, "eeeewq", "jgftft", 880, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(7, "01/08/2019", [new VincentsTransaction(789, "iughff", "opoiii", 125, "btc"), new VincentsTransaction(988, "aqQQQQ", "trewew", 01, "eth"), new VincentsTransaction(432, "eeeee", "khuuuu", 40, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(8, "01/09/2019", [new VincentsTransaction(890, "sdsrer", "sdfser", 99, "eth"), new VincentsTransaction(886, "gfgfdg", "qqqqqq", 88, "eth"), new VincentsTransaction(444, "gfgfd", "llllkl", 70, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(9, "01/10/2019", [new VincentsTransaction(901, "mnghjy", "dfgxbg", 65, "btc"), new VincentsTransaction(644, "dddsds", "wwwwww", 55, "eth"), new VincentsTransaction(333, "sdsaqq", "ererew", 50, "eth")]));
blockChain.createAdditionalBlock(new VincentsBlock(10, "01/11/2019", [new VincentsTransaction(012, "vccvff", "uiyfvv", 74, "btc"), new VincentsTransaction(994, "mnmnmm", "qqqqhh", 66, "eth"), new VincentsTransaction(323, "qwqwqq", "wreret", 30, "eth")]));
 
console.log(JSON.stringify(blockChain, null, 2)); // let's view entire blockchain
 
console.log('Validate entire blockchain: ' + blockChain.isBlockChainValid()); // let's validate the blockchain is secure
 
blockChain.chain[5].hash = blockChain.chain[5].calculateBlockHash();  // let's try to recalculate hash for block 5
 
console.log('Is blockchain valid? ' + blockChain.isBlockChainValid()); 

Alright, let’s run this bad boy and see the blockchain we created.

{
  "chain": [
    {
      "blockIndex": 0,
      "blockCreatedWhen": "01/01/2019",
      "blockTransactions": "Initial Block",
      "blockPreviousHash": "",
      "hash": "46d4d81e6047cccb6e856a4bc800ed344fbe4b78df5f5a7fe5862e8773cd022a",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      }
    },
    {
      "blockIndex": 1,
      "blockCreatedWhen": "01/02/2019",
      "blockTransactions": [
        {
          "transactionId": 123,
          "inputAccount": "abcxyz",
          "outputAccount": "xyzabc",
          "fee": 30,
          "amount": "btc",
          "hash": "324cc491e4436b69299a905847124308c6dfc272642d9dbb3808bd79048bc110"
        },
        {
          "transactionId": 999,
          "inputAccount": "uyyuyy",
          "outputAccount": "xxdzkj",
          "fee": 550,
          "amount": "btc",
          "hash": "3beef24348997907eaa0263d3eb1393b1e74cb365e730649c60a910ecbbee0d5"
        },
        {
          "transactionId": 653,
          "inputAccount": "drerea",
          "outputAccount": "kioolk",
          "fee": 70,
          "amount": "eth",
          "hash": "a30e34266150f7b616aa4ebe88461406308280c9821425dbe0bfbc1fa7e6843a"
        }
      ],
      "blockPreviousHash": "46d4d81e6047cccb6e856a4bc800ed344fbe4b78df5f5a7fe5862e8773cd022a",
      "hash": "54ee7657f991b1341ecfa7d2ecfe7cf0501751f147ecc7b9ca08b2354068eeab",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 2,
      "blockCreatedWhen": "01/03/2019",
      "blockTransactions": [
        {
          "transactionId": 234,
          "inputAccount": "sfgfsd",
          "outputAccount": "rrttyu",
          "fee": 50,
          "amount": "eth",
          "hash": "f2378fced4de261dc5c531441d867b385f5726b76eb76d6ece8b739de3f6d2f7"
        },
        {
          "transactionId": 555,
          "inputAccount": "iuiuii",
          "outputAccount": "rrttyu",
          "fee": 50,
          "amount": "eth",
          "hash": "cb42ae591f275f7d265f749489c0830ef985252d256ad176430a9acee0b7c525"
        },
        {
          "transactionId": 553,
          "inputAccount": "hghghg",
          "outputAccount": "ffgfff",
          "fee": 80,
          "amount": "eth",
          "hash": "edb71da69f72d01fdefe7939665d8fc59489bb16e5f3d7e662a187b1d437ef8f"
        }
      ],
      "blockPreviousHash": "54ee7657f991b1341ecfa7d2ecfe7cf0501751f147ecc7b9ca08b2354068eeab",
      "hash": "f58b63c0fbe00f69b6b1bd04560ffdd72ebe7b71e70a16224bf45aad01308e0f",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 3,
      "blockCreatedWhen": "01/04/2019",
      "blockTransactions": [
        {
          "transactionId": 345,
          "inputAccount": "srthhf",
          "outputAccount": "oouyuu",
          "fee": 65,
          "amount": "btc",
          "hash": "eaa995a8b3a64237c3133fbb744ed1761ba716781b7026f7f956043173c452f6"
        },
        {
          "transactionId": 452,
          "inputAccount": "jhghgg",
          "outputAccount": "rrttyu",
          "fee": 11,
          "amount": "eth",
          "hash": "e867bcef38e0272776fc3fbeff0aac19cb366ca513945ddfa1491adc2f3257b2"
        },
        {
          "transactionId": 230,
          "inputAccount": "wewfgf",
          "outputAccount": "ghjgtt",
          "fee": 230,
          "amount": "eth",
          "hash": "d25b62651513ee902e063970b5b7baed30de4f9832b7a78db3247a09414a1495"
        }
      ],
      "blockPreviousHash": "f58b63c0fbe00f69b6b1bd04560ffdd72ebe7b71e70a16224bf45aad01308e0f",
      "hash": "288b9f37d503b22a5f4535e086ab84fdbff2e22f8880fb2f24baa29b5151235d",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 4,
      "blockCreatedWhen": "01/05/2019",
      "blockTransactions": [
        {
          "transactionId": 456,
          "inputAccount": "sfgfss",
          "outputAccount": "xzsdee",
          "fee": 4,
          "amount": "btc",
          "hash": "af15f83e9c599347351019f62309fb1b9077447a4e0fc8b48a6b5c487b1e144e"
        },
        {
          "transactionId": 780,
          "inputAccount": "fgtfdd",
          "outputAccount": "rrttyu",
          "fee": 22,
          "amount": "eth",
          "hash": "8984871129b02f0b09f83abd5c1161f6a0dee64f84c336a54f5c34e5454f02a7"
        },
        {
          "transactionId": 112,
          "inputAccount": "qwewue",
          "outputAccount": "hgyuyu",
          "fee": 280,
          "amount": "eth",
          "hash": "2631aa030dfbc44fe084d86f69c1d24ca64a154c59d13b42718211ed02e3b1dc"
        }
      ],
      "blockPreviousHash": "288b9f37d503b22a5f4535e086ab84fdbff2e22f8880fb2f24baa29b5151235d",
      "hash": "07205c43afea9e53d02dedce994c891babccd8397d082b431f986045cbc18e44",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 5,
      "blockCreatedWhen": "01/06/2019",
      "blockTransactions": [
        {
          "transactionId": 567,
          "inputAccount": "xxcbbf",
          "outputAccount": "nbvbcx",
          "fee": 545,
          "amount": "eth",
          "hash": "8030161e3fdb7038fb7e751236063996152897f9647c654fb47334da7f7295bb"
        },
        {
          "transactionId": 677,
          "inputAccount": "fdfsaa",
          "outputAccount": "uytttt",
          "fee": 33,
          "amount": "eth",
          "hash": "b327dfa8769ec04bc447313af98feeb783c95c198e926737ea916700f4b71994"
        },
        {
          "transactionId": 111,
          "inputAccount": "hjhjh",
          "outputAccount": "huiuii",
          "fee": 5480,
          "amount": "eth",
          "hash": "aae165434e054c42e7da129b08a7c99f6c544351b7383459e322ef253570f4a4"
        }
      ],
      "blockPreviousHash": "07205c43afea9e53d02dedce994c891babccd8397d082b431f986045cbc18e44",
      "hash": "55c88c98e497a9f300ca3ec8bec0129652a8e5e9b49e6ecaf4ab0c63b42ebf4f",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 6,
      "blockCreatedWhen": "01/07/2019",
      "blockTransactions": [
        {
          "transactionId": 678,
          "inputAccount": "uiyuyy",
          "outputAccount": "dfgree",
          "fee": 5,
          "amount": "btc",
          "hash": "134269524a221afb1f5ef218584b063ab4bea3aaa5dc2cdbfa66f439f2d1e36b"
        },
        {
          "transactionId": 553,
          "inputAccount": "ooouio",
          "outputAccount": "yuyuuu",
          "fee": 55,
          "amount": "eth",
          "hash": "19076e1cb35d8357b16f92794c5bd1ff020c8cb9e8ce5fcf03b560256a363c16"
        },
        {
          "transactionId": 467,
          "inputAccount": "eeeewq",
          "outputAccount": "jgftft",
          "fee": 880,
          "amount": "eth",
          "hash": "461ad65962d2d1cc1f767c1b9c0f569d19ef48be60ef2fe8c08898cc01d34492"
        }
      ],
      "blockPreviousHash": "55c88c98e497a9f300ca3ec8bec0129652a8e5e9b49e6ecaf4ab0c63b42ebf4f",
      "hash": "e1087468c2719f967584cab0a22938b81e9e956762f2c5a2d2dd91da2c92cfbd",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 7,
      "blockCreatedWhen": "01/08/2019",
      "blockTransactions": [
        {
          "transactionId": 789,
          "inputAccount": "iughff",
          "outputAccount": "opoiii",
          "fee": 125,
          "amount": "btc",
          "hash": "7149930eae17b35f22c02acb0765b829d79e5539c6e2e80b837045f89d0422c2"
        },
        {
          "transactionId": 988,
          "inputAccount": "aqQQQQ",
          "outputAccount": "trewew",
          "fee": 1,
          "amount": "eth",
          "hash": "d752f91eb8010b5c9d6066afb92a5fa6c4667f9fc18b6f8d4a7c1a32b104919c"
        },
        {
          "transactionId": 432,
          "inputAccount": "eeeee",
          "outputAccount": "khuuuu",
          "fee": 40,
          "amount": "eth",
          "hash": "c5c20ac19253cd6782f0a95eb628c719cafeac22d4c8bacbf2863b06e0e366db"
        }
      ],
      "blockPreviousHash": "e1087468c2719f967584cab0a22938b81e9e956762f2c5a2d2dd91da2c92cfbd",
      "hash": "63302ff671cee7c659e1bf9eb1cd659f054d4615c4692d5b425ad04b2f82deb6",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 8,
      "blockCreatedWhen": "01/09/2019",
      "blockTransactions": [
        {
          "transactionId": 890,
          "inputAccount": "sdsrer",
          "outputAccount": "sdfser",
          "fee": 99,
          "amount": "eth",
          "hash": "c4abc25fcc9ea1e78be488aac5ee9a3ee1f16b0915e23700ff6bb11e1df02c51"
        },
        {
          "transactionId": 886,
          "inputAccount": "gfgfdg",
          "outputAccount": "qqqqqq",
          "fee": 88,
          "amount": "eth",
          "hash": "fd454dbdfb263db527ed335116aab73a7dab8468d3d443aa0fd8e4c7e438f465"
        },
        {
          "transactionId": 444,
          "inputAccount": "gfgfd",
          "outputAccount": "llllkl",
          "fee": 70,
          "amount": "eth",
          "hash": "c9b9ebdcb469f0f5ae8c6653c10f45d88a59b807c87b9febe1be986844d558f4"
        }
      ],
      "blockPreviousHash": "63302ff671cee7c659e1bf9eb1cd659f054d4615c4692d5b425ad04b2f82deb6",
      "hash": "fec255eb642f1dd02ab7c5185bfd78f9574b50c0188a888b4227b8cef5497e0e",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 9,
      "blockCreatedWhen": "01/10/2019",
      "blockTransactions": [
        {
          "transactionId": 901,
          "inputAccount": "mnghjy",
          "outputAccount": "dfgxbg",
          "fee": 65,
          "amount": "btc",
          "hash": "6e94502eb38d14410141d87bd27a2369e14e62bf8efece8adbde9873a8e88777"
        },
        {
          "transactionId": 644,
          "inputAccount": "dddsds",
          "outputAccount": "wwwwww",
          "fee": 55,
          "amount": "eth",
          "hash": "7072d7ec51bf41a1f36744f7abf8e9e4f70d195b708420f77b5141bcb7567f45"
        },
        {
          "transactionId": 333,
          "inputAccount": "sdsaqq",
          "outputAccount": "ererew",
          "fee": 50,
          "amount": "eth",
          "hash": "199c710224da1e16f597c2eae088acd5c3d4b6fd9a12d84c0b76a735eed541a2"
        }
      ],
      "blockPreviousHash": "fec255eb642f1dd02ab7c5185bfd78f9574b50c0188a888b4227b8cef5497e0e",
      "hash": "fcec05a7f1afb3c91ddbf90f36e04d17e4eabd7e47545a9f08173767cd4d74c8",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    },
    {
      "blockIndex": 10,
      "blockCreatedWhen": "01/11/2019",
      "blockTransactions": [
        {
          "transactionId": 10,
          "inputAccount": "vccvff",
          "outputAccount": "uiyfvv",
          "fee": 74,
          "amount": "btc",
          "hash": "8f2abd539ef073b7d4053fe6090196f682f6361a619329e45a3a0df10919623c"
        },
        {
          "transactionId": 994,
          "inputAccount": "mnmnmm",
          "outputAccount": "qqqqhh",
          "fee": 66,
          "amount": "eth",
          "hash": "040dda42beee5673e882884e3e963292015253348b1db5c3feb5d54af4e4b728"
        },
        {
          "transactionId": 323,
          "inputAccount": "qwqwqq",
          "outputAccount": "wreret",
          "fee": 30,
          "amount": "eth",
          "hash": "af54b136d57904e80823c53649d4149092fb6ebb4bf1e8578facaae8aca2cf1c"
        }
      ],
      "blockPreviousHash": "fcec05a7f1afb3c91ddbf90f36e04d17e4eabd7e47545a9f08173767cd4d74c8",
      "hash": "9074846c6a4153802d86cd19b6d95266c56d082329c6f0f52ded270fae269c48",
      "nonce": 0,
      "merkleTreeRoot": {
        "words": [
          -474954686,
          -1728308204,
          -1694763832,
          -1720731356,
          665731556,
          1687917388,
          -1533699813,
          2018687061
        ],
        "sigBytes": 32
      },
      "index": null
    }
  ]
}

NOTE: Within the merkleTreeRoot property, crypto-js utilizes word arrays encoded as UTF-8 when given a string.

Above, notice the hash and blockPreviousHash property of each block. This serves as the link for the chain.

But what happens if one were to modify a block somehow? Perhaps change the fee property or attempt to recalculate a block hash?

console.log('Validate entire blockchain: ' + blockChain.isBlockChainValid()); // let's validate the blockchain is secure
 
blockChain.chain[5].hash = blockChain.chain[5].generateBlockHash();  // let's try to recalculate hash for block 5
 
console.log('Is blockchain valid? ' + blockChain.isBlockChainValid()); 
 
Validate entire blockchain: true
Is blockchain valid? false

It appears that the blockchain validation function isBlockChainValid() caught an attempt to recalculate its hash. Of course, this is pretty basic validation, but it serves its purpose to illustrate the secure nature of blockchain.

Final Thoughts

In summary, a blockchain can be written in various languages. I hope this basic JavaScript version not only illustrates that but gives a little more overview of how blockchains work.

Thank for reading ! Please share if you liked it!

How do I build an HTML solution in Solidity

There is a code for a simple conversion (Farenheit to Celcius) in HTML. I am working to recreate the same thing in Solidity. I would need some pointers in making it work. The solidity Code is as follows:&nbsp;

There is a code for a simple conversion (Farenheit to Celcius) in HTML. I am working to recreate the same thing in Solidity. I would need some pointers in making it work. The solidity Code is as follows: 


contract TemperatureSolution{
    uint16 input,
function convertTemp(uint16 _input) public{
    return (document.getElementById("outputCelcius").innerHTML=(valNum-32)/1.8)
}
convertTemp(_input);

}

For reference, the HTML that it is based upon is as follows (this works, but I intend to create it on a blockchain):

<html>
<body>
<p>Type a value in the Fahrenheit field to convert the value to Celsius:</p>
<p>
<label>Fahrenheit</label>
<input id="inputFahrenheit" type="number" placeholder="Fahrenheit" oninput="temperatureConverter(this.value)" onchange="temperatureConverter(this.value)">
</p>
<p>Celcius: <span id="outputCelcius"></span></p>

&lt;script&gt;
function temperatureConverter(valNum) {

valNum = parseFloat(valNum);
document.getElementById("outputCelcius").innerHTML=(valNum-32)/1.8;
}
</script>
</body>


JavaScript Tutorial: if-else Statement in JavaScript

JavaScript Tutorial: if-else Statement in JavaScript

This JavaScript tutorial is a step by step guide on JavaScript If Else Statements. Learn how to use If Else in javascript and also JavaScript If Else Statements. if-else Statement in JavaScript. JavaScript's conditional statements: if; if-else; nested-if; if-else-if. These statements allow you to control the flow of your program's execution based upon conditions known only during run time.

Decision Making in programming is similar to decision making in real life. In programming also we face some situations where we want a certain block of code to be executed when some condition is fulfilled.
A programming language uses control statements to control the flow of execution of the program based on certain conditions. These are used to cause the flow of execution to advance and branch based on changes to the state of a program.

JavaScript’s conditional statements:

  • if
  • if-else
  • nested-if
  • if-else-if

These statements allow you to control the flow of your program’s execution based upon conditions known only during run time.

  • if: if statement is the most simple decision making statement. It is used to decide whether a certain statement or block of statements will be executed or not i.e if a certain condition is true then a block of statement is executed otherwise not.
    Syntax:
if(condition) 
{
   // Statements to execute if
   // condition is true
}

Here, condition after evaluation will be either true or false. if statement accepts boolean values – if the value is true then it will execute the block of statements under it.
If we do not provide the curly braces ‘{‘ and ‘}’ after if( condition ) then by default if statement will consider the immediate one statement to be inside its block. For example,

if(condition)
   statement1;
   statement2;

// Here if the condition is true, if block 
// will consider only statement1 to be inside 
// its block.

Flow chart:

Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate If statement 

var i = 10; 

if (i > 15) 
document.write("10 is less than 15"); 

// This statement will be executed 
// as if considers one statement by default 
document.write("I am Not in if"); 

< /script> 

Output:

I am Not in if
  • if-else: The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But what if we want to do something else if the condition is false. Here comes the else statement. We can use the else statement with if statement to execute a block of code when the condition is false.
    Syntax:
if (condition)
{
    // Executes this block if
    // condition is true
}
else
{
    // Executes this block if
    // condition is false
}


Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate If-else statement 

var i = 10; 

if (i < 15) 
document.write("10 is less than 15"); 
else
document.write("I am Not in if"); 

< /script> 

Output:

i is smaller than 15
  • nested-if A nested if is an if statement that is the target of another if or else. Nested if statements means an if statement inside an if statement. Yes, JavaScript allows us to nest if statements within if statements. i.e, we can place an if statement inside another if statement.
    Syntax:
if (condition1) 
{
   // Executes when condition1 is true
   if (condition2) 
   {
      // Executes when condition2 is true
   }
}

Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate nested-if statement 

var i = 10; 

if (i == 10) { 

// First if statement 
if (i < 15) 
	document.write("i is smaller than 15"); 

// Nested - if statement 
// Will only be executed if statement above 
// it is true 
if (i < 12) 
	document.write("i is smaller than 12 too"); 
else
	document.write("i is greater than 15"); 
} 
< /script> 

Output:

i is smaller than 15
i is smaller than 12 too
  • if-else-if ladder Here, a user can decide among multiple options.The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
if (condition)
    statement;
else if (condition)
    statement;
.
.
else
    statement;


Example:

<script type = "text/javaScript"> 
// JavaScript program to illustrate nested-if statement 

var i = 20; 

if (i == 10) 
document.wrte("i is 10"); 
else if (i == 15) 
document.wrte("i is 15"); 
else if (i == 20) 
document.wrte("i is 20"); 
else
document.wrte("i is not present"); 
< /script> 

Output:

i is 20