node.js （节点：2684）UnhandledPromiseRejectionWarning：未处理的承诺拒绝（拒绝ID：1）：TypeError：无法读取未定义的属性“then”
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(node:2684) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): TypeError: Cannot read property 'then' of undefined
提问by Harsimer
I am using .then for first time, instead of .then I use callback function.
我第一次使用 .then，而不是 .then 我使用回调函数。
Below is my code snippet:
下面是我的代码片段：
phantom.create().then(function (ph) {
ph.createPage().then(function (page) {
page.open("http://codebeautify.org/xmlvalidator").then(function (status) {
page.render(base_pdf_path + lpnumber + '.pdf').then(function () {
console.log('PDF generated for waybill');
//Insert waybill url in db.
return waybill_url.insertWaybillUrl('Lpsimer', waybillUrl).then(function (waybill_inserted_resp) {
callback(null, true);
}).catch(function (error) {
callback(err_waybill_inserted);
});
});
});
});
});
The above function is calling a function which is as below, this is in another file and called properly filename is waybill.js:
上面的函数正在调用一个如下的函数，这是在另一个文件中并且正确调用文件名是waybill.js：
var mongoose = require('mongoose');
var q = require('promised-io/promise');
var WaybillUrlSchema = new mongoose.Schema({
lpnumber: String,
url: String,
waybilltime: Date
});
module.exports = {
insertWaybillUrl: function (lpnumber, url) {
var defer = q.defer();
var waybill_insert = new waybill_url({
lpnumber: lpnumber,
url: url,
waybilltime: new Date()
});
//Save model to MongoDB
waybill_insert.save(function (err, inserted_waybill) {
if (err) {
return defer.reject(err);
}
else {
return defer.resolve(inserted_waybill);
}
});
}
};
Previously I was using this pattern to make callbacks and it was working fine:
以前我使用这种模式进行回调，它工作正常：
waybill_url.insertWaybillUrl('Lpsimer', waybillUrl, function(err, success) {
if (err) {
} else {
}
)}
Now I have to use .then due to usage of phantom code to write PDF and it has made the job cumbersome.
现在我必须使用 .then 由于使用幻影代码来编写 PDF 并且它使工作变得繁琐。
Need suggestion on how I can make callbacks within callbacks.
需要关于如何在回调中进行回调的建议。
UPDATE
更新
phantom.create().then(function (ph) {
ph.createPage().then(function (page) {
page.open("http://codebeautify.org/xmlvalidator").then(function (status) {
page.render(base_pdf_path + lpnumber + '.pdf').then(function () {
//Insert waybill url in db.
waybill_url.insertWaybillUrl('Lpsimer', waybillUrl).then(function (waybill_inserted_resp) {
if (waybill_inserted_resp) {
callback(null, true);
}
}).catch(function (error_waybill_url_insert) {
console.log("Error in inserting waybill:" + err_waybill_inserted);
callback(error_waybill_url_insert);
});
}).catch(function (error_render) {
console.log("error_render");
callback(error_render);
});
}).catch(function (error_open) {
callback(error_open);
});
}).catch(function (error_create_page) {
callback(error_create_page);
});
}).catch(function (error_phantom_create) {
callback(error_phantom_create);
});
Now I have added catch for every then as suggested by rsp in his answer, but now I am getting error which I have catched and send to another callback:
现在我按照 rsp 在他的回答中的建议为每个 then 添加了 catch ，但是现在我收到错误，我已经捕获并发送到另一个回调：
Cannot read property 'then' of undefined
无法读取未定义的属性“then”
I am getting this error where I have added console.log("error_render"); that is where I am calling page.render function of phantom.
我在添加 console.log("error_render"); 的地方遇到了这个错误。那就是我调用phantom的page.render函数的地方。
My requirement is simple. I want to generate a PDF file using phantom and then I just want to call another function which is in another file waybill_url, function name: waybill_url.insertWaybillUrl. But due to callbacks and asynchronous behaviour this simple calling of two functions is getting cumbersome.
我的要求很简单。我想使用phantom生成一个PDF文件，然后我只想调用另一个文件waybill_url中的另一个函数，函数名称：waybill_url.insertWaybillUrl。但是由于回调和异步行为，这两个函数的简单调用变得很麻烦。
回答by rsp
Make sure that you use catch()and not only then()- or two arguments to then(). Otherwise you will not handle errors and you will get that warning - which will be an error, not a warning, in next versions of Node.
确保您使用catch()and 而不仅仅是then()- 或两个参数到then(). 否则，您将无法处理错误，并且会收到该警告 - 在 Node.js 的下一个版本中，这将是错误，而不是警告。
See this answer for more info about it:
有关它的更多信息，请参阅此答案：
