Node.js res.send VS res.end VS返回res.end
我有以下代码在mongodb findAndUpdateOne更新查询中有一个语法错误。
router.post('/buylicense', isLoggedIn, function(req, res) { if (!req.body.cid) { return res.send('failed'); } Company.findOne({ ownedBy: req.user.local.username, _id: req.body.cid }, function(err, result) { if (err) { return res.send('failed'); } if (result.license) { return res.send('valid'); } else { Company.findOneAndUpdate({ ownedBy: req.user.local.username, _id: req.body.cid }, { license: true, licenseExpireDate: { $add: ["$date", 3 * 24 * 60 * 60000] // bad code, a problem for another day } }, function(err) { if (err) { console.log(err); return res.end('failed'); // Code should stop here. } console.log('got here'); return res.send('success'); }); } }); console.log('How did I get here?'); res.send('failed'); }); 我的问题是为什么代码到达代码的最后部分：
console.log('How did I get here?'); res.send('failed');
如果我使用除了return res.end以外的任何其他代码达到最后，崩溃我的应用程序。 只是做res.end不起作用，也不return res.send 。 不应该return或至lessres.end足以实际上停止代码到达最后？
显示错误如果我不停止错误right way ，可能不相关，但在这里是：
How did I get here? { CastError: Cast to date failed for value "[object Object]" at path "licenseExpireDate" at MongooseError.CastError (/media/node_modules/mongoose/lib/error/cast.js:19:11) at SchemaDate.cast (/media/node_modules/mongoose/lib/schema/date.js:242:9) at SchemaDate.castForQuery (/media/node_modules/mongoose/lib/schema/date.js:276:17) at Query._castUpdateVal (/media/node_modules/mongoose/lib/query.js:2477:17) at Query._walkUpdatePath (/media/node_modules/mongoose/lib/query.js:2372:25) at Query._castUpdate (/media/node_modules/mongoose/lib/query.js:2296:23) at castDoc (/media/node_modules/mongoose/lib/query.js:2500:18) at Query._findAndModify (/media/node_modules/mongoose/lib/query.js:1755:17) at Query._findOneAndUpdate (/media/node_modules/mongoose/lib/query.js:1622:8) at /media/node_modules/kareem/index.js:156:8 at args (/media/node_modules/kareem/index.js:71:20) at Query.<anonymous> (/media/node_modules/mongoose/lib/schema.js:728:7) at next (/media/node_modules/kareem/index.js:82:14) at Kareem.execPre (/media/node_modules/kareem/index.js:99:3) at Kareem.wrap (/media/node_modules/kareem/index.js:146:8) at Query._findOneAndUpdate (/media/node_modules/kareem/index.js:188:11) message: 'Cast to date failed for value "[object Object]" at path "licenseExpireDate"', name: 'CastError', kind: 'date', value: { '$add': [ '$date', 259200000 ] }, path: 'licenseExpireDate', reason: undefined } got here _http_outgoing.js:346 throw new Error('Can\'t set headers after they are sent.'); ^ Error: Can't set headers after they are sent. at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:346:11) at ServerResponse.header (/media/node_modules/express/lib/response.js:718:10) at ServerResponse.send (/media/node_modules/express/lib/response.js:163:12) at /media/sf_vShared/xyz/app/modalRoutes.js:461:28 at /media/node_modules/kareem/index.js:160:11 at Query._findAndModify (/media/node_modules/mongoose/lib/query.js:1767:14) at Query._findOneAndUpdate (/media/node_modules/mongoose/lib/query.js:1622:8) at /media/node_modules/kareem/index.js:156:8 at args (/media/node_modules/kareem/index.js:71:20) at Query.<anonymous> (/media/node_modules/mongoose/lib/schema.js:728:7) at next (/media/node_modules/kareem/index.js:82:14) at Kareem.execPre (/media/node_modules/kareem/index.js:99:3) at Kareem.wrap (/media/node_modules/kareem/index.js:146:8) at Query._findOneAndUpdate (/media/node_modules/kareem/index.js:188:11) at Query.findOneAndUpdate (/media/node_modules/mongoose/lib/query.js:1611:15) at Function.Model.findOneAndUpdate (/media/node_modules/mongoose/lib/model.js:1491:13) [nodemon] app crashed - waiting for file changes before starting...
拳头让我们看看三个ExpressJSfunction之间有什么区别
res.end：来自NodeJS核心。 在Express JS中，如果您需要快速结束请求并且不需要发送任何数据，那么您可以使用此function
res.send：发送数据并结束请求
res.json以JSON格式发送数据并结束请求。
我的问题是为什么代码到达代码的最后部分：？
我希望你知道JavaScript是asynchronous语言。 所有使用Mongoose调用MongoDB的数据库都是asynchronous的。 所以Compnay.findOne是一个asynchronous的函数调用，它停留在事件循环直到数据库读取操作没有完成。 作为JS的asynchronous行为，JS主线程执行不会等待DB函数的结果返回（无阻塞）并到达最后一行，因为您的请求以调用res.end("failed")但是当DB读取操作完成返回数据，然后再次调用res.send并以Error: Can't set headers after they are sent.结束Error: Can't set headers after they are sent.
希望这可以帮助 ：）