Blockchain JS运行报TypeError:无法读取undefined的length属性

报错和JavaScript版本迭代、语法兼容无关，是代码中两处笔误导致：

• Blockchain类构造函数名拼写错误：JavaScript类构造函数的固定命名为constructor，代码中错写为contstructor（字母s、t顺序颠倒），实例化Blockchain时初始化逻辑未执行，this.chain属性从未被赋值。
• getLatestBlock方法缺少返回语句：方法体内仅编写了取链尾区块的表达式，未通过return返回结果，方法默认返回undefined，后续访问.hash属性时相当于读取undefined的属性，直接触发运行时错误。

const SHA256 = require("crypto-js/sha256");

class Block {
  constructor(index, timestamp, data, previousHash = "") {
    this.index = index;
    this.timestamp = timestamp;
    this.data = data;
    this.previousHash = previousHash;
    this.hash = this.calculateHash();
  }

  calculateHash() {
    return SHA256(
      this.index +
        this.previousHash +
        this.timestamp +
        JSON.stringify(this.data)
    ).toString();
  }
}

class Blockchain {
  constructor() {
    this.chain = [this.createGenesisBlock()];
  }

  createGenesisBlock() {
    return new Block(0, "01/01/2017", "Genesis block", "0");
  }

  getLatestBlock() {
    return this.chain[this.chain.length - 1];
  }

  addBlock(newBlock) {
    newBlock.previousHash = this.getLatestBlock().hash;
    newBlock.hash = newBlock.calculateHash();
    this.chain.push(newBlock);
  }
}

let savejeeCoin = new Blockchain();
savejeeCoin.addBlock(new Block(1, "10/07/2017", { amount: 4 }));
savejeeCoin.addBlock(new Block(2, "12/07/2017", { amount: 10 }));

console.log(JSON.stringify(savejeeCoin, null, 4));

内容的提问来源于stack exchange，提问作者Sheroze Mohammed