javascript - 当我使用另一个模块类时，如何修复 "TypeError: Right-hand side of ' instanceof' is not callable"？

Question

我试图检查上下文的类型是否是另一个文件中的上下文实例，但是 Node js 抛出 TypeError: Right-hand side of 'instanceof' is not callable.

index.js

const Transaction = require('./Transaction');

class Context {
    constructor(uid) {
        if (typeof uid !== 'string')
            throw new TypeError('uid must be a string.');

        this.uid = uid;
    }

    runTransaction(operator) {
        return new Promise((resolve, reject) => {
            if (typeof operator !== 'function')
                throw new TypeError('operator must be a function containing transaction.');

            operator(new Transaction(this))
        });
    }
}

module.exports = Context;

Transaction.js

const Context = require('./index');

class Transaction {
    constructor(context) {
        // check type
        if (!(context instanceof Context))
            throw new TypeError('context should be type of Context.');

        this.context = context;
        this.operationList = [];
    }

    addOperation(operation) {

    }
}

module.exports = Transaction;

另一个js文件

let context = new Context('some uid');
context.runTransaction((transaction) => {
});

然后，它抛出 TypeError: Right-hand side of 'instanceof' is not callable。

Answer 1

问题是您有一个循环依赖。另一个文件需要 index，index 需要 Transaction，而 Transaction 需要 index。因此，当 transaction 运行时，它会尝试请求 index，其模块已经在构建过程中。 index 尚未导出任何内容，因此此时需要它会导致一个空对象。

因为两者必须相互调用，解决它的一种方法是将两个类放在一起，然后将它们都导出:

// index.js
class Context {
  constructor(uid) {
    if (typeof uid !== "string") throw new TypeError("uid must be a string.");

    this.uid = uid;
  }

  runTransaction(operator) {
    return new Promise((resolve, reject) => {
      if (typeof operator !== "function")
        throw new TypeError(
          "operator must be a function containing transaction."
        );

      operator(new Transaction(this));
    });
  }
}

class Transaction {
  constructor(context) {
    // check type
    if (!(context instanceof Context))
      throw new TypeError("context should be type of Context.");

    this.context = context;
    this.operationList = [];
    console.log("successfully constructed transaction");
  }

  addOperation(operation) {}
}

module.exports = { Context, Transaction };

和

const { Context, Transaction } = require("./index");
const context = new Context("some uid");
context.runTransaction(transaction => {});

https://codesandbox.io/s/naughty-jones-xi1q4