javascript - 使事件发射器同步

Question

我正在试用包 proxy-lists ，它使用事件发射器来接收代理。

我创建了以下示例:

const ProxyLists = require('proxy-lists');

function main() {

    const options = {
        countries: null
    };

    // `gettingProxies` is an event emitter object.
    const gettingProxies = ProxyLists.getProxies(options);

    let data = []
    gettingProxies.on('data', function (proxies) {
        console.log(proxies);
        data.push(proxies)
        if (data.length > 1000) {
            return data
        }
    });
}

console.log("First Call");
const res = main()
console.log(res);
console.log("Last Call");

但是，我收到以下输出:

First Call
undefined
Last Call
[ { ipAddress: 'ip-192-169-156-211.ip.secureserver.net',
    port: 52324,
    country: null,
    source: 'rosinstrument' },
  { ipAddress: 'ip-192-169-218-61.ip.secureserver.net',

如您所见，函数运行时已调用 console.log。但是，我更喜欢以下同步顺序:

First Call
[ { ipAddress: '72.89.213.193.static.cust.telenor.com',
    port: 51024,
    country: 'us',
    source: 'rosinstrument' },
  { ipAddress: '50.250.56.129',
    port: 48380,
    country: 'us',
    source: 'rosinstrument' },
...
Last Call

对我做错了什么有什么建议吗？

Answer 1

我认为您可以将异步代码包装到 Promise 中，并使用您正在等待的值resolve 它，然后然后 调用您需要的下一个代码，如下所示:

const ProxyLists = require('proxy-lists');

function main() {
    return new Promise((resolve, reject) => {
        const options = {
            countries: null
        };

        // `gettingProxies` is an event emitter object.
        const gettingProxies = ProxyLists.getProxies(options);

        let data = []

        gettingProxies.on('data', function (proxies) {
            console.log(proxies);
            data.push(proxies)
            if (data.length > 1000) {
                resolve(data);
            }
        });
    })
}

console.log("First Call");

main().then((res) => {
    console.log(res);
    console.log("Last Call");
})

如果你正在使用 babel 或 typescript 之类的东西，你甚至可以像这样以其他方式使用 async/await:

console.log("First Call");
var res = await main();
console.log(res);
console.log("Last Call");