[英]async for await logic return issue
所以我在試圖弄清楚如何修復下面的剪輯時遇到了一些問題。 截至目前,它正在運行 for 循環的 'request(scanurl,.....' 部分之前返回值。循環確實運行。此外,我不認為 'lines200' var 正在通過櫃台。我是一個學習者,所以任何解釋都將不勝感激。
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)
}
});
電流輸出:
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
當您有一個包含異步操作的循環時,您有兩個選擇之一。 您可以並行運行它們,並以某種方式跟蹤它們何時全部完成。 或者,您可以一個接一個地依次運行它們。 看來您的循環可以以任何一種方式構建,但我將說明順序選項。
async/await
的出現允許我們在中間使用適當的await
來“暫停” for
循環。 但是,為了做到這一點,所有異步操作都必須基於承諾,以便您可以await
這些承諾。 為此,我已從request()
庫切換到request-promise-native
庫,它是使用原生內置承諾的request
庫的承諾包裝器。 它還有另一個不錯的功能,它會自動檢查 2xx 狀態代碼,因此您不必自己這樣做。
下面是代碼的樣子:
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);
}
});
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