如何在客户端中从 Meteor.call() 分配外部值？

Question

我的情况与中所述类似。定义了一个服务器 Meteor 方法，该方法接收调用第三方库以交换结果的对象。在客户端调用 Meteor.call 时，我需要将结果值分配给外部变量。但是，我的操作方式变得不确定（我想这是因为该方法的异步行为）我如何改进以下代码？

//Method on the client side (React.JS Component)
callRatesConvert(fromCurrency, toCurrency, amount) {
    const call = this.props.call;
    let resCall = 0; // Outer variable
    let settings = {};
    settings.fromCurrency = fromCurrency;
    settings.toCurrency = toCurrency;
    settings.amount = amount;
    settings.accuracy = 10;

//Calls Backend method API that returns res successfully
    call('rates.convert', settings, (err, res) => {
        if (err) {
           //Shows UI Error to user
        } else if (res) { //res value is fetched from backend method properly
            resCall = res; // this is not being assigning properly
        }
    });
    console.log('resCall', resCall); //this prints 'undefined'
    return resCall;
    }

Answer 1

将 callRatesConvert 转换为 returns Promise 的函数。如果需要，您还可以使用 shorthand 属性赋值来减少代码的语法噪音：

callRatesConvert(fromCurrency, toCurrency, amount) {
  const call = this.props.call;
  const settings = {
    fromCurrency,
    toCurrency ,
    amount,
    accuracy: 10,
  };
  return new Promise((resolve, reject) => {
    call('rates.convert', settings, (err, res) => {
      if (err) {
        //Show Error UI to user
        reject(err);
      } else if (res) {
        resolve(res);
      }
    });
  });
}

然后与

一起食用

someInstantiation.callRatesConvert(...)
  .then((resCall) => {
    // do something with the response
  });

Answer 2

你那里有问题，不是在调用中，而是在你的代码上，我会添加一些注释。

//Method on the client side (React.JS Component)
callRatesConvert(fromCurrency, toCurrency, amount) {
    const call = this.props.call;
    let resCall = 0; // Outer variable
    let settings = {};
    settings.fromCurrency = fromCurrency;
    settings.toCurrency = toCurrency;
    settings.amount = amount;
    settings.accuracy = 10;

//Calls Backend method API that returns res succesfully
    call('rates.convert', settings, (err, res) => {
        if (err) {
           //Show Error UI to user
        } else if (res) { //res value is fetched from backend method properly
            console.log('result from call', res) //this wont be undefined.
            resCall = res; //this is assigned but it takes some time because it is still fetching
        }
    });
    console.log('resCall', resCall); //this will print undefined because it is outside the call method, and it is not assigned yet.
    return resCall; // this obviously will be undefined.
    }

所以一种解决方案可能是使用来自 meteor 的 Session：

//Method on the client side (React.JS Component)
callRatesConvert(fromCurrency, toCurrency, amount) {
    const call = this.props.call;
    let resCall = 0; // Outer variable
    let settings = {};
    settings.fromCurrency = fromCurrency;
    settings.toCurrency = toCurrency;
    settings.amount = amount;
    settings.accuracy = 10;

//Calls Backend method API that returns res succesfully
    call('rates.convert', settings, (err, res) => {
        if (err) {
           //Show Error UI to user
        } else if (res) { 
            resCall = res; 
            console.log('resCall', resCall); 
            Session.set("resCall", resCall)
        }
    });
    }

希望对您有所帮助。

如何在客户端中从 Meteor.call() 分配外部值？

How to assign outer value from Meteor.call() in client?

javascript

asynchronous

meteor