TypeError: Cannot read property 'then' of undefined in Algorithmic Trading

Question

出于某种原因，每次我运行这段代码时，我都会遇到“类型错误：无法读取未定义的属性 'then'”错误。我不明白为什么。这是代码：

console.log("BUY");
exchange.marketBuy()
.then(res => {
console.log("Buy successful");
hasPosition = true
setTimeout(strategy, 1000)
})
.catch(console.error);

marketBuy() 函数是

    marketBuy() {
    client.getLatestInformation()
    .then(response => {
      var price = response.result[0].last_price;
      client.placeActiveOrder({
       side: "Buy",
       symbol: "BTCUSD",
       order_type: "Market",
       qty: 20,
       time_in_force: "GoodTillCancel",
       take_profit: price * 1.5,
       stop_loss: price / 1.5})
      .then(response => console.log(response))

    })

我试过了

console.log("BUY");
exchange.marketBuy()
.then(res => {
hasPosition = true
setTimeout(strategy, 1000)
return Promise.resolve(console.log("Buy successful"));
})
.catch(console.error);

我似乎找不到问题所在。有什么想法吗？

Answer 1

您有几个不同的问题。正如其他人已经指出的那样，您没有从 makeBuy() 方法返回承诺。但是，它似乎并不像建议的那样简单地添加一个 return 语句那么容易。这是因为在将 hasPosition 设置为 true 之前，您似乎实际上需要等待内部承诺从 client.placeActiveOrder() 解决。

所以你有两个选择（推荐#2）：

将必须等待内部 promise 解析的代码移动到内部 promise 的 .then() 因此（这会产生 hasPosition 变量本身的问题）：

client.placeActiveOrder({
       side: "Buy",
       symbol: "BTCUSD",
       order_type: "Market",
       qty: 20,
       time_in_force: "GoodTillCancel",
       take_profit: price * 1.5,
       stop_loss: price / 1.5})
      .then(response => {
         console.log(response);
         console.log("Buy successful");
         hasPosition = true;
         setTimeout(strategy, 1000);
         });

使用async/await让您的代码读起来像一个工作流程：

    async marketBuy() {
      const response = await client.getLatestInformation();
      const price = response.result[0].last_price;
      const order = await client.placeActiveOrder({
        side: "Buy",
        symbol: "BTCUSD",
        order_type: "Market",
        qty: 20,
        time_in_force: "GoodTillCancel",
        take_profit: price * 1.5,
        stop_loss: price / 1.5
      })
      return order;
    }

推荐选择二，因为它允许您按照预期的方式编写代码。下面是不会再抛出错误的调用代码：

    console.log("BUY");
    exchange.marketBuy()
      .then(res => { // res here is the order returned
        console.log("Buy successful");
        hasPosition = true
        setTimeout(strategy, 1000)
      })
      .catch(console.error);

TypeError: Cannot read property 'then' of undefined in Algorithmic Trading

TypeError: Cannot read property 'then' of undefined in Algorithmic Trading

javascript

algorithmic-trading