Wrong function isChainValid() about savjeecoin HOT 9 CLOSED

<select id="dif">
    <option value="3">Difficulty 3</option>
    <option value="4">Difficulty 4</option>
    <option value="5">Difficulty 5</option>
    <option value="6">Difficulty 6</option>
</select>
<select id="trans">
    <option value="3">3 Transactions</option>
    <option value="5">5 Transactions</option>
    <option value="10">10 Transactions</option>
    <option value="20">20 Transactions</option>
    <option value="40">40 Transactions</option>
    <option value="100">100 Transactions</option>
</select>

<input id="startDemo" type="button" value="Start demo" onclick="startDemo(document.getElementById('dif').value, document.getElementById('trans').value)"/>
<input id="clearDemo" type="button" value="Clear screen" onclick="overide()" />

<p id="chainlog"></p>

<script type="text/javascript">
    function overide() {
        document.getElementById('chainlog').innerHTML = "";
        console.clear();
    }

    function startDemo(dif, trans) {
        document.getElementById('chainlog').innerHTML = "<h3>Demo run log</h3>";

        const SHA256 = CryptoJS.SHA256;

        class Block {
            constructor(index, timestamp, data, previousHash = '') {
                this.index = index;
                this.timestamp = timestamp;
                this.data = data;
                this.previousHash = previousHash;
                this.nonce = 0;
                this.hash = this.calculateHash(); 
            }
            calculateHash() {
                return SHA256(this.index + this.timestamp + JSON.stringify(this.data) + this.previousHash + this.nonce).toString();
            }
            mineBlock(difficulty) {
                while (this.hash.substring(0, difficulty) != Array(difficulty + 1).join("0")) {
                    this.nonce++;
                    this.hash = this.calculateHash();
                }
                document.getElementById('chainlog').innerHTML += "Block mined --> Hash: <b>" + this.hash + "</b>, Nonce: <b>" + this.nonce + "</b>";
                console.log("Block mined! - Hash: " + this.hash + ", Nonce: " + this.nonce);
            }
        }
        class Blockchain {
            constructor(difficulty, transnr) {
                this.chain = [this.createGenesisBlock()];
                this.difficulty = difficulty;
                document.getElementById('chainlog').innerHTML += "Created the chain with difficulty (number of leading zeros in hash): " + this.difficulty + "<br/>";
                console.log("Created the chain with difficulty (number of leading zeros in hash): " + this.difficulty);
                document.getElementById('chainlog').innerHTML += "Added the Genesis block (the first block that can be used to start previous hash chain), Chain length: " + this.chain.length + "<br/>Creating and adding " + transnr + " transactions<br/>";
                console.log("Added the Genesis block (the first block that can be used to start previous hash chain), Chain length: " + this.chain.length);
            }
            createGenesisBlock() {
                return new Block(0, "2018/01/01", "Genesis Block", "0");
            }
            getLatestBlock() {
                return this.chain[this.chain.length - 1];
            }
            addBlock(newBlock) {
                newBlock.previousHash = this.getLatestBlock().hash;
                newBlock.mineBlock(this.difficulty);
                this.chain.push(newBlock);
                document.getElementById('chainlog').innerHTML += ", Chain length: <b>" + chain.chain.length + "</b><br/>";

            }
            ischainValid() {
                for (let i = 1; i < this.chain.length; i++) {
                    let currentBlock = this.chain[i];
                    let previousBlock = this.chain[i - 1];
                    if (currentBlock.hash != currentBlock.calculateHash()) {
                        return false;
                    }
                    if (currentBlock.previousHash != previousBlock.calculateHash()) {
                        document.getElementById('chainlog').innerHTML += "Prev hash: <b>" + currentBlock.previousHash + "</b>, Calc prev hash: " + previousBlock.calculateHash() + "<br/>";
                        return false;
                    }
                }
                return true;
            }

            displayAccounts(size) {
                var accountsDebet = new Array(size);
                var accountsCredit = new Array(size);
                var debnr, crenr, amnr;

                for (let n = 0; n < size; n++) {
                    accountsDebet[n] = 0;
                    accountsCredit[n] = 0;
                }
                for (let i = 1; i < this.chain.length; i++) {
                    debnr = parseInt(this.chain[i].data.debetaccount) % 1000;
                    crenr = parseInt(this.chain[i].data.creditaccount) % 1000;
                    amnr = parseInt(this.chain[i].data.amount);
                    accountsDebet[debnr - 1] = amnr + parseInt(accountsDebet[parseInt(this.chain[i].data.debetaccount) % 1000 - 1]);
                    accountsCredit[crenr - 1] = amnr + parseInt(accountsCredit[parseInt(this.chain[i].data.creditaccount) % 1000 - 1]);
                }

                for (let n = 0; n < size; n++) {
                    document.getElementById('chainlog').innerHTML += "Account: 100" + (n + 1) + ", Debet: " + accountsDebet[n] + ", Credit: " + accountsCredit[n] + ", Ballance: " + (parseInt(accountsDebet[n]) - parseInt(accountsCredit[n])) + "<br/>";
                }

            }
        }

        // *****************************************************************************************
        // THIS IS WHERE YOU SET YOUR DIFFICULTY AND HOW MANY TRANSACTIONS YOU WANT TO SIMULATE
        // *****************************************************************************************
        var difficulty = parseInt(dif); 		// SET DIFICULITY FOR NUMBER OF PRE-SEEDING ZEROS IN HASH! (1,2,3 = miliseconds | 4 = seconds | 5 = minutes | 6 = doze off | 7 = go home (this script will probably run dry by now of integers in nonce value) | 8 = not this week | 9 = months | 10 = go die in peace | 11)
        var transactions = parseInt(trans); 	// SET HOW MANY TRANSACTIONS YOU WANT TO SIMULATED
        // *****************************************************************************************

        let chain = new Blockchain(difficulty, transactions);
        var timestart;
        var timeend;
        var timestamp;
        var am;
        var deb;
        var cre;

        timestart = new Date().getTime();
        document.getElementById('chainlog').innerHTML += "<h3>Transactions</h3>";

        for (var i = 1; i < transactions + 1; i++) {
            if(i>1) document.getElementById('chainlog').innerHTML += "------------------------------------------<br/>";
            console.log("---");
            am = Math.floor(Math.random() * 50) + 1;        // SET HOW BIG A RANDOM AMOUNT YOU WANT TO TRANSFER -> RANDOM() * 50 + 1 = FROM 1 TO 50
            deb = Math.floor(Math.random() * 5) + 1001;     // SET A RANDOM DEBIT ACCOUNT TO TRANSFER AMOUNT TO -> RANDOM() * 5 + 1001 = FROM 1001 TO 1005
            cre = Math.floor(Math.random() * 5) + 1001;     // SET A RANDOM CREDIT ACCOUNT TO TRANSFER AMOUNT FROM -> RANDOM() * 5 + 1001 = FROM 1001 TO 1005
            timestamp = new Date().getTime();
            document.getElementById('chainlog').innerHTML += "Block created --> Block ID: <b>" + i + "</b>, Timestamp: <b>" + timestamp + "</b>, Amount: <b>" + am + "</b>, Debet account: <b>" + deb + "</b>, Credit account: <b>" + cre + "</b><br/>";
            console.log("Block created, Block ID: " + i + ", Timestamp: " + timestamp + ", Amount: " + am + ", Debet account: " + deb + ", Credit account: " + cre);
            console.log("... Mining block, please wait ... ");
            chain.addBlock(new Block(i, timestamp, { amount: am, debetaccount: deb, creditaccount: cre }));
        }

        timeend = new Date().getTime();
        var timed = timeend - timestart;

        document.getElementById('chainlog').innerHTML += "<h3>Time spend mining and validating</h3>";
        document.getElementById('chainlog').innerHTML += "Mining time: " + Math.floor(timed / 60000) + " min , " + Math.floor(timed % 60000 / 1000) + " sec , " + Math.floor(timed % 1000) + " mili<br/>";
        console.log("Mining time: " + Math.floor(timed / 60000) + " min , " + Math.floor(timed % 60000 / 1000) + " sec , " + Math.floor(timed % 1000) + " mili");
        timestart = new Date().getTime();
        document.getElementById('chainlog').innerHTML += "Is chain valid: " + chain.ischainValid() + "<br/>";
        console.log("Is chain valid: " + chain.ischainValid());
        timeend = new Date().getTime();
        timed = timeend - timestart;
        document.getElementById('chainlog').innerHTML += "Validating time: " + Math.floor(timed / 60000) + " min , " + Math.floor(timed % 60000 / 1000) + " sec , " + Math.floor(timed % 1000) + " mili<br/>";
        console.log("Validating time: " + Math.floor(timed / 60000) + " min , " + Math.floor(timed % 60000 / 1000) + " sec , " + Math.floor(timed % 1000) + " mili");
        document.getElementById('chainlog').innerHTML += "<h3>Accounts overview after transactions</h3>";
        chain.displayAccounts(5);

    }
</script>
<h3>Descriptions</h3>
<ul>
    <li>Each transaction is moving a random amount (1-50) from one of 5 accounts to another (1001-1005)</li>
    <li>Minning: Each transaction is hashed and the content including previous hash is mathematical crushed in to a hex number</li>
    <li>A number called Nonce is initiated to 1 and incremented by one until the hash have the desired leading zeros, trial and error method</li>
    <li>So basically, the Nonce represents how many times the hashing mecanism had to run until the block was succesfully mined</li>
</ul>
<i>* Thanks to Savjee for basic js code from https://github.com/SavjeeTutorials/SavjeeCoin/</i>