Javascript 异步等待逻辑返回问题
因此,我有一些问题,试图找出如何修复下面的剪报。到目前为止,它在for of循环的'request(scanurl,…'部分运行之前返回值。循环确实运行。此外,我不认为'lines200'变量正在通过计数器更新。我是一名学习者,因此任何解释都将不胜感激Javascript 异步等待逻辑返回问题,javascript,node.js,async-await,Javascript,Node.js,Async Await,因此,我有一些问题,试图找出如何修复下面的剪报。到目前为止,它在for of循环的'request(scanurl,…'部分运行之前返回值。循环确实运行。此外,我不认为'lines200'变量正在通过计数器更新。我是一名学习者,因此任何解释都将不胜感激 async function processLineByLine(baseData) { console.log('enter async func') try { const fileStream = fs.createReadSt
async function processLineByLine(baseData) {
console.log('enter async func')
try {
const fileStream = fs.createReadStream('./file.txt');
let linesTotal = 0;
let lines200 = 0;
const rl = readline.createInterface({
input: fileStream
});
for await (let line of rl) {
console.log('in loop')
const scanurl = (baseData.match(/http/gi)) ? (baseData) : ('https://' + baseData + line);
linesTotal++;
request(scanurl, {json: true}, function (error, response, body) {
let statusCode = response.statusCode;
let htmlBody = body;
//console.log(htmlBody)
//console.log(statusCode)
if (statusCode == "200") {
console.log('in 2nd if')
let $ = cheerio.load(htmlBody);
let titleScrape = $('title').html();
console.log(titleScrape)
if (titleScrape.match(/404 | test/gi)) {
console.log('Matched')
} else {
lines200++;
console.log(lines200)
}
} else {
// Do nothing
}
});
}
return {
total: linesTotal,
count200: lines200,
};
} catch (error) {
console.error(error)
}
}
router.get('/:reqTarget', async (req, res) => {
console.log('starting')
var baseUrl = req.params.reqTarget;
try {
console.log('in the try')
const initTest = await processLineByLine(baseUrl);
const {total, count200} = initTest;
console.log(total, count200)
if (initTest) return res.status(200).send({
message: 'STATUS 200 COUNT: ' + count200 + ' ' + 'TOTAL: ' + total });
} catch (error) {
console.log(error)
}
});
电流输出:
starting
in the try
enter async func
in loop
in loop
in loop
in loop
in loop
in loop
in loop
33 0 //this is the return that is two early
in 2nd if
404 | test
Matched
in 2nd if
404 | test
Matched
当你有一个包含异步操作的循环时,你有两个选项中的一个。你可以并行运行它们,并以某种方式跟踪它们的完成时间。或者,你可以一个接一个地顺序运行它们。看起来你的循环可以以任何一种方式构造,但我将演示顺序选项 <>代码< Acthc/AsAs/<代码>的出现,允许我们在适当的<代码> > <代码>中间暂停“<代码> < /COD>循环”。但是,为了做到这一点,所有异步操作都必须是基于承诺的,因此您可以“<代码>等待< /CODE >这些承诺。为此,我已经从<代码>请求()切换。library到
request-promise-native
库,该库是request
库的承诺包装器,使用本机内置承诺。它还有另一个很好的功能,可以自动检查2xx状态代码,因此您无需自己进行检查
下面是该代码的外观:
const rp = require('request-promise-native');
async function processLineByLine(baseData) {
console.log('enter async func')
try {
const fileStream = fs.createReadStream('./file.txt');
let linesTotal = 0;
let lines200 = 0;
const rl = readline.createInterface({
input: fileStream
});
for await (let line of rl) {
console.log('in loop')
const scanurl = (baseData.match(/http/gi)) ? (baseData) : ('https://' + baseData + line);
linesTotal++;
try {
let htmlBody = await rp(scanurl, {json: true});
let $ = cheerio.load(htmlBody);
let titleScrape = $('title').html();
console.log(titleScrape);
if (titleScrape.match(/404 | test/gi)) {
console.log('Matched')
} else {
lines200++;
console.log(lines200)
}
} catch(e) {
console.log(`error on request(${scanurl})`, e);
// like your original code, this will only log the error
// and then continue with the rest of the URLs
}
}
return {
total: linesTotal,
count200: lines200,
};
} catch (error) {
console.error(error)
}
}
router.get('/:reqTarget', async (req, res) => {
console.log('starting')
var baseUrl = req.params.reqTarget;
try {
console.log('in the try')
const initTest = await processLineByLine(baseUrl);
const {total, count200} = initTest;
console.log(total, count200)
res.status(200).send({message: 'STATUS 200 COUNT: ' + count200 + ' ' + 'TOTAL: ' + total});
} catch (error) {
console.log(error)
res.sendStatus(500);
}
});
request(scanurl,{json:true},函数(错误、响应、正文){
是异步的……你不需要等待它开始,更不用说完成了……await
并没有神奇地等待异步代码完成,它在等待一个承诺——而你没有承诺被请求者返回。现在有一个版本的问题每天被问10次。也许这是重复,但现在比以前更疯狂这过去是因为人们现在显然认为async
或await
具有神奇的能力,可以知道何时完成了基于回调的异步操作(提示它们不-async
函数仅在与异步操作的完成相关的承诺下使用await
时才有帮助).代替等待,可以使用setTimeoutfunction@LDS那是个糟糕的建议