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如何用JS構建你自己的區塊鏈，針對這個問題，這篇文章詳細介紹了相對應的分析和解答，希望可以幫助更多想解決這個問題的小伙伴找到更簡單易行的方法。
區塊鏈太復雜，那我們就講點簡單的。用JS來構建你自己的區塊鏈系統，寥寥幾行代碼就可以說明區塊鏈的底層數據結構、POW挖礦思想和交易過程等。當然了，真實的場景遠遠遠比這復雜。小編的目的僅限于讓大家初步了解、初步認識區塊鏈。
區塊鏈顧名思義是由區塊連接而成的鏈，因此最基本的數據結構是Block。每個Block都含有timestamp、data、hash、previousHash等信息。其中data用來存儲數據，previousHash是前一個區塊的hash值。示意如下：
hash是對區塊信息的摘要存儲，hash的好處是任意長度的信息經過hash都可以映射成固定長度的字符串，如可用sha256：
calculateHash() {
return SHA256(this.previousHash + this.timestamp + JSON.stringify(this.data)).toString();
}Block的最基本數據結構如下：
class Block {
constructor(timestamp, data, previousHash = '') {
this.timestamp = timestamp;
this.data = data;
this.previousHash = previousHash;
//對hash的計算必須放在最后，保證所有數據賦值正確后再計算
this.hash = this.calculateHash();
}
calculateHash() {
return SHA256(this.previousHash + this.timestamp + JSON.stringify(this.data)).toString();
}
}多個Block鏈接而成BlockChain，顯然可用用數組或鏈表來表示，如：
class BlockChain {
constructor() {
this.chain = [];
}
}正所謂萬物始于一，區塊鏈的第一個區塊總是需要人為來手動創建，這個區塊的previousHash為空，如：
createGenesisBlock() {
return new Block("2018-11-11 00:00:00", "Genesis block of simple chain", "");
}區塊鏈的構造方法也應改為：
class BlockChain {
constructor() {
this.chain = [this.createGenesisBlock()];
}
}每新加一個區塊，必須保證與原有區塊鏈連接起來，即：
class BlockChain {
getLatestBlock() {
return this.chain[this.chain.length - 1];
}
addBlock(newBlock) {
//新區塊的前一個hash值是現有區塊鏈的最后一個區塊的hash值；
newBlock.previousHash = this.getLatestBlock().hash;
//重新計算新區塊的hash值（因為指定了previousHash)；
newBlock.hash = newBlock.calculateHash();
//把新區塊加入到鏈中；
this.chain.push(newBlock);
}
...
}區塊鏈數據結構的核心是保證前后鏈接、無法篡改，但是如果有人真的篡改了某個區塊，我們該如何校驗發現呢？最笨也是最自然是想法就是遍歷所有情況，逐一校驗，如：
isChainValid() {
//遍歷所有區塊
for (let i = 1; i < this.chain.length; i++) {
const currentBlock = this.chain[i];
const previousBlock = this.chain[i - 1];
//重新計算當前區塊的hash值，若發現hash值對不上，說明該區塊有數據被篡改，hash值未重新計算
if (currentBlock.hash !== currentBlock.calculateHash()) {
console.error("hash not equal: " + JSON.stringify(currentBlock));
return false;
}
//判斷當前區塊的previousHash是否真的等于前一個區塊的hash，若不等，說明前一個區塊被篡改，雖然hash值被重新計算正確，但是后續區塊的hash值并未重新計算，導致整個鏈斷裂
if (currentBlock.previousHash !== previousBlock.calculateHash) {
console.error("previous hash not right: " + JSON.stringify(currentBlock));
return false;
}
}
return true;
}跑起來看看，即：
let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));
console.log(JSON.stringify(simpleChain, null, 4));
console.log("is the chain valid? " + simpleChain.isChainValid());結果如下：
ali-186590cc4a7f:simple-chain shanyao$ node main_1.js
{
"chain": [
{
"timestamp": "2018-11-11 00:00:00",
"data": "Genesis block of simple chain",
"previousHash": "",
"hash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89"
},
{
"timestamp": "2018-11-11 00:00:01",
"data": {
"amount": 10
},
"previousHash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89",
"hash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529"
},
{
"timestamp": "2018-11-11 00:00:02",
"data": {
"amount": 20
},
"previousHash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529",
"hash": "274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"
}
]
}
is the chain valid? true注意看其中的previousHash與hash，確實是當前區塊的previousHash指向前一個區塊的hash。
都說區塊鏈不可篡改，是真的嗎？讓我們篡改第2個區塊試試，如：
let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));
console.log("is the chain valid? " + simpleChain.isChainValid());
//將第2個區塊的數據，由10改為15
simpleChain.chain[1].data = {amount: 15};
console.log("is the chain still valid? " + simpleChain.isChainValid());
console.log(JSON.stringify(simpleChain, null, 4));結果如下：
ali-186590cc4a7f:simple-chain shanyao$ node main_1.js
is the chain valid? true
hash not equal: {"timestamp":"2018-11-11 00:00:01","data":{"amount":15},"previousHash":"fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89","hash":"150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529"}
is the chain still valid? false
{
"chain": [
{
"timestamp": "2018-11-11 00:00:00",
"data": "Genesis block of simple chain",
"previousHash": "",
"hash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89"
},
{
"timestamp": "2018-11-11 00:00:01",
"data": {
"amount": 15
},
"previousHash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89",
"hash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529"
},
{
"timestamp": "2018-11-11 00:00:02",
"data": {
"amount": 20
},
"previousHash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529",
"hash": "274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"
}
]
}顯然，篡改了數據之后，hash值并未重新計算，導致該區塊的hash值對不上。
那么，如果我們聰明點，篡改后把hash值也重新計算會如何？
let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));
console.log("is the chain valid? " + simpleChain.isChainValid());
//篡改后重新計算hash值
simpleChain.chain[1].data = {amount: 15};
simpleChain.chain[1].hash = simpleChain.chain[1].calculateHash();
console.log("is the chain still valid? " + simpleChain.isChainValid());
console.log(JSON.stringify(simpleChain, null, 4));結果如下：
ali-186590cc4a7f:simple-chain shanyao$ node main_1.js
is the chain valid? true
previous hash not right: {"timestamp":"2018-11-11 00:00:02","data":{"amount":20},"previousHash":"150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529","hash":"274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"}
is the chain still valid? false
{
"chain": [
{
"timestamp": "2018-11-11 00:00:00",
"data": "Genesis block of simple chain",
"previousHash": "",
"hash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89"
},
{
"timestamp": "2018-11-11 00:00:01",
"data": {
"amount": 15
},
"previousHash": "fd56967ff621a4090ff71ce88fdd456547d1c92d2e93766b7e8791f7a5f91f89",
"hash": "74d139274fb692495b7c805dd5822faa0c5b5e6058b6beef96e87e18ab83a6b1"
},
{
"timestamp": "2018-11-11 00:00:02",
"data": {
"amount": 20
},
"previousHash": "150b196268a0152e9f0e719ac131a722472a809f49bd507965029a78c7400529",
"hash": "274a7a13ed20118e8cb745654934a7e24a4d59333ba17dfbf5d4cfe0fa8a6e34"
}
]
}顯然，第3個區塊的previousHash并未指向第2個區塊的hash。
其實并不是，如果我們再聰明一點，把后續區塊的hash值也重新計算一下，不就OK了嗎？ 確實如此，如：
let simpleChain = new BlockChain();
simpleChain.addBlock(new Block("2018-11-11 00:00:01", {amount: 10}));
simpleChain.addBlock(new Block("2018-11-11 00:00:02", {amount: 20}));
console.log("is the chain valid? " + simpleChain.isChainValid());
//篡改第2個區塊
simpleChain.chain[1].data = {amount: 15};
simpleChain.chain[1].hash = simpleChain.chain[1].calculateHash();
//并把第3個區塊也重新計算
simpleChain.chain[2].previousHash = simpleChain.chain[1].hash;
simpleChain.chain[2].hash = simpleChain.chain[2].calculateHash();
console.log("is the chain still valid? " + simpleChain.isChainValid());
console.log(JSON.stringify(simpleChain, null, 4關于如何用JS構建你自己的區塊鏈問題的解答就分享到這里了，希望以上內容可以對大家有一定的幫助，如果你還有很多疑惑沒有解開，可以關注億速云行業資訊頻道了解更多相關知識。
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