Javascript 使用导出函数时无法读取未定义的属性
我有以下Express应用程序: router.jsJavascript 使用导出函数时无法读取未定义的属性,javascript,node.js,ecmascript-5,Javascript,Node.js,Ecmascript 5,我有以下Express应用程序: router.js var express = require('express'); var router = express.Router(); var exch = require("../exchanges/exch")(); router.get('/', function(req, res, next) { exch .getTicker((tick) => { res.send('get ticker exch:
var express = require('express');
var router = express.Router();
var exch = require("../exchanges/exch")();
router.get('/', function(req, res, next) {
exch .getTicker((tick) => {
res.send('get ticker exch: ' + JSON.stringify(tick));
});
});
module.exports = router;
var Kraken = require('kraken-api');
var moment = require('moment');
var _ = require('lodash');
/**
...code
**/
var Exchange = function(config) {
_.bindAll(this);
if(_.isObject(config)) {
this.key = config.key;
this.secret = config.secret;
this.currency = config.currency.toUpperCase()
this.asset = config.asset.toUpperCase();
}
this.pair = addPrefix(this.asset) + addPrefix(this.currency);
this.name = 'kraken';
this.since = null;
this.kraken = new Kraken(this.key, this.secret);
}
Exchange.prototype.getTicker = function(callback) {
var set = function(err, data) {
if(!err && _.isEmpty(data))
err = 'no data';
else if(!err && !_.isEmpty(data.error))
err = data.error;
if (err)
return console.log('unable to get ticker' + JSON.stringify(err));
var result = data.result[this.pair];
var ticker = {
ask: result.a[0],
bid: result.b[0]
};
callback(err, ticker);
};
this.kraken.api('Ticker', {pair: this.pair}, _.bind(set, this));
};
}
module.exports = Exchange;
exch.js
var express = require('express');
var router = express.Router();
var exch = require("../exchanges/exch")();
router.get('/', function(req, res, next) {
exch .getTicker((tick) => {
res.send('get ticker exch: ' + JSON.stringify(tick));
});
});
module.exports = router;
var Kraken = require('kraken-api');
var moment = require('moment');
var _ = require('lodash');
/**
...code
**/
var Exchange = function(config) {
_.bindAll(this);
if(_.isObject(config)) {
this.key = config.key;
this.secret = config.secret;
this.currency = config.currency.toUpperCase()
this.asset = config.asset.toUpperCase();
}
this.pair = addPrefix(this.asset) + addPrefix(this.currency);
this.name = 'kraken';
this.since = null;
this.kraken = new Kraken(this.key, this.secret);
}
Exchange.prototype.getTicker = function(callback) {
var set = function(err, data) {
if(!err && _.isEmpty(data))
err = 'no data';
else if(!err && !_.isEmpty(data.error))
err = data.error;
if (err)
return console.log('unable to get ticker' + JSON.stringify(err));
var result = data.result[this.pair];
var ticker = {
ask: result.a[0],
bid: result.b[0]
};
callback(err, ticker);
};
this.kraken.api('Ticker', {pair: this.pair}, _.bind(set, this));
};
}
module.exports = Exchange;
正如您所看到的,我通过require(“…”)
包含对象。但是,我仍然得到以下错误:
无法读取未定义的属性“getTicker”
TypeError:无法读取未定义的属性“getTicker”
在/home/ubuntu/workspace/routes/ticker.js:20:9
在Layer.handle[作为handle_请求](/home/ubuntu/workspace/node_modules/express/lib/router/Layer.js:95:5)
下一步(/home/ubuntu/workspace/node_modules/express/lib/router/route.js:137:13)
在Route.dispatch(/home/ubuntu/workspace/node_modules/express/lib/router/Route.js:112:3)
在Layer.handle[作为handle_请求](/home/ubuntu/workspace/node_modules/express/lib/router/Layer.js:95:5)
在/home/ubuntu/workspace/node_modules/express/lib/router/index.js:281:22
在Function.process_参数(/home/ubuntu/workspace/node_modules/express/lib/router/index.js:335:12)
下一步(/home/ubuntu/workspace/node_modules/express/lib/router/index.js:275:10)
在Function.handle(/home/ubuntu/workspace/node_modules/express/lib/router/index.js:174:3)
在路由器上(/home/ubuntu/workspace/node_modules/express/lib/router/index.js:47:12)
为什么会发生此错误?我如何修复它?您没有创建实例,因此无法访问原型上的方法。实际上,您只是调用了由
exch.js
导出的构造函数Exchange
。由于直接调用构造函数时不返回任何内容(隐式未定义),因此会出现以下错误:
var exch = require("../exchanges/exch")(); //exch is undefined because Exchange as a function returns nothing
这不会设置原型,因为您没有构造对象,只是调用了函数。相反,使用new
构建一个新的Exchange
对象:
var Exchange = require("../exchanges/exch");
var exch = new Exchange();
这将创建一个新的Exchange
对象,您可以在其中从原型调用getTicker
。注意:确保将config
传递给构造函数
如果没有new
,您可以在Exchange
中进行检查,查看是否在没有new
的情况下意外调用了它,并返回一个新实例:
var Exchange = function(config) {
if(!(this instanceof Exchange)) {
return new Exchange(config);
}
//...
}
这样做的目的是返回Exchange
的新实例,即使您直接调用了该函数。现在您可以使用:
var exch = require("../exchanges/exch")();
但是我总是更喜欢前一种方法,即总是为构造函数使用new
。require(“../exchanges/exch”)()
调用函数而不是创建新实例,使用new
实例化以使用原型。您得到未定义
的原因是交换
不返回任何内容。您假设它是一个构造函数
,但您将其称为函数
请改用代码:
var exchModule = require("../exchanges/exch")
var exch=new exchModule()
更改exch.js中代码的最后一行
exports.exchange = Exchange;
现在在router.js中进行修改
var exch = require("../exchanges/exch").exchange;
var exchObject= new exch();
现在您可以使用exchObject对象来调用方法,感谢您突出显示它,我不知道它。