Node JS 如何从函数的回调函数访问全局变量？

Question

我正在使用 NodeJS 进行事件捕获。 所有的调用都将来到 getme 函数。 从这个函数我调用 getUserLocation() 函数，它返回基于 ip 的地理位置。 如何根据此值更新全局变量？

var getClientAddress = function (req) {
return (req.get('x-forwarded-for') || '').split(',')[0]  || req.connection.remoteAddress;
}

var getClientLocation = function (ipaddress, callback) {
    freegeoip.getLocation(ipaddress, function(err, location) {
        if (err) throw err;
        return callback(location);
    });
}

var store = [{'hello': 'world', 'country': 'India', 'City': 'Indupur'}];

for (eve=0;eve<store.length;eve++){
if(!store[eve].lat){
        clientIp = getClientAddress(req);
        getClientLocation("XXX:XX:XX:XXX", function(resp) {
            console.log(resp);
            store[eve].country = store[eve].country || resp.country_name;
            store[eve].region = store[eve].region || resp.region_name;
            store[eve].city = store[eve].city || resp.city;
            store[eve].lat = store[eve].lat || resp.latitude;
            store[eve].lng =  store[eve].lng || resp.longitude;
        });

    }

但是商店无法访问。 它是未定义的。 如何更新商店？

实际代码：这是实际代码：

https://github.com/Gowtham95india/CapVengine/blob/master/server.js

这是错误消息：

Server started! At http://localhost:8080
Redis started! Ready to perform
{ e: '[{"device_id":"dsfkdjf-dsfdls-fejfskj-e2oiej2j3jf","user_id":2124,"email":"gowtham95india@gmail.com","event_properties":{"utm_source":"HelloWorld"}, "lat":""}]',
  v: 2 }
2017-02-11T09:02:10.838Z


{ ip: '121.244.122.142',
  country_code: 'IN',
  country_name: 'India',
  region_code: 'MH',
  region_name: 'Maharashtra',
  city: 'Phursungi',
  zip_code: '412308',
  time_zone: 'Asia/Kolkata',
  latitude: 18.4667,
  longitude: 73.9833,
  metro_code: 0 }
/Users/GowthamSai/Documents/repo/capeve/server.js:111
                store[eve].country = store[eve].country || resp.country_name;
                                               ^

TypeError: Cannot read property 'country' of undefined
    at /Users/GowthamSai/Documents/repo/capeve/server.js:111:48
    at /Users/GowthamSai/Documents/repo/capeve/server.js:36:16
    at Request._callback (/Users/GowthamSai/Documents/repo/capeve/node_modules/node-freegeoip/lib/freegeoip.js:25:16)
    at Request.self.callback (/Users/GowthamSai/Documents/repo/capeve/node_modules/request/request.js:187:22)
    at emitTwo (events.js:106:13)
    at Request.emit (events.js:191:7)
    at Request.<anonymous> (/Users/GowthamSai/Documents/repo/capeve/node_modules/request/request.js:1048:10)
    at emitOne (events.js:96:13)
    at Request.emit (events.js:188:7)
    at IncomingMessage.<anonymous> (/Users/GowthamSai/Documents/repo/capeve/node_modules/request/request.js:969:12)
    at emitNone (events.js:91:20)
    at IncomingMessage.emit (events.js:185:7)
    at endReadableNT (_stream_readable.js:974:12)
    at _combinedTickCallback (internal/process/next_tick.js:74:11)
    at process._tickCallback (internal/process/next_tick.js:98:9)

Answer 1

您的问题不在于访问store 。 该全局变量已定义。

你的问题是访问store[eve]因为你从来没有定义过。

您直接尝试读取store[eve].lat而无需为store[eve]分配任何内容（例如使用store[eve] = store[eve] || {} ）。

---

您还有其他一些问题，它们是该问题的根本原因，解释如下：

• 如何从异步调用返回响应？
• 循环内的 JavaScript 闭包——简单实用的例子