I created an App that processes students results by extracting data from multiple excel workbooks. The problem is that using Puppeteer to generate the PDF files, throws the system into a loop till it hangs the system.
Actually, I have tested same codes below using PhantomJs which is bundled as pdf-creator-node, and was able to generate 150 PDF files comfortably in 3 minutes. The only challenge I dumped PhantomJs is that all the styling in the CSS file was not included, even when I inserted it as an inline style in the header, suing replace function of JS. Another, is that PhantomJs is no longer in active development. I searched the web, and found out that only Puppeteer is the valid solution with active development and support too.
I tried using page.close() at the end of pdfCreator() which is in a loop, and browser.close() at the end of pdfGenerator(). What I am doing wrong?
Here below are the codes in the server.js and PdfGenerator.js files, with a sample of the ERROR, and screenshot of my Task Manager after the system crawled out of hanging state. For HTML generation, I used Mustache. I excluded some lines of codes in server.js because the total character count was over 60k.
server.js
// [codes were removed here]
if(getCode == 'compute-result') {
// declare variable
let setData = null;
let setTitle = 'Results Computation...';
let setArgs = getArgs;
// dataFromFile = ReadFile(pathCodeTextFile);
// setArgs = Number(dataFromFile);
setCode = 'compute-result';
let setView = [];
let setNext = true;
let countTerms = [];
// if(getArg > 0) {
// Final Result computation
const getJson = ReadFile(pathJsonResults);
// const getCtrl = ReadFile(pathJsonCtrl);
const getResultObject = JSON.parse(getJson);
getResult = getResultObject;
const totalResults = getResult.firstTerm.length + getResult.secondTerm.length + getResult.thirdTerm.length;
if(setView.length < 1 && getResult != null) {
setData = 'PDFs for Students Results initiating...';
setView.unshift('Reading saved data...');
client.emit('query', {data: setData, title: setTitle, code: setCode, next: setNext, args: null, view: JSON.stringify(setView)});
}
Sleep(2000).then(() => {
if(getResult != null) {
setData = 'Students Results will be ready in a moment';
client.emit('query', {data: setData, title: setTitle, code: setCode, next: setNext, args: setArgs, view: JSON.stringify(setView)});
}
const wacthFiles = (file, className, termName, sessionName, completed, pdfList) => {
try {
if(typeof file == 'string' && !FileExists(pathJsonPdfList)) {
if(pdfList.length < 2){
setData = 'Saving PDFs to downladable files...';
}
if(className != null && termName != null && sessionName != null) {
setTitle = `${pdfList.length} Result PDF${pdfList.length > 1?'s':''}...`;
setView.unshift(file);
if(!countTerms.includes(termName)) {
countTerms.push(termName)
}
// setCode = -1000 - pdfList.length;
// console.log('PDF PROGRESS: ', `${pdfList.length} Result PDF${pdfList.length > 1?'s':''}... ${setCode}`);
// when all PDFs are created
if(completed) {
setTitle = setTitle.replace('...', ' [completed]');
setData = 'Result Download button is Active. You may click it now.';
setView.unshift('=== PDF GENERATION COMPLETED ===');
setView.unshift(`A total of ${pdfList.length} students' Results were generated`);
WriteFile(pathJsonPdfList, JSON.stringify(pdfList));
// set donwload button active
setCode = Number(codeTextFilePdfCompleted);
setNext = false;
getResult = null;
let termString = countTerms.toString();
termString = ReplaceAll(termString, '-term', '');
termString = ReplaceAll(termString, ',', '-');
const addTxt = `${className} _${termString} Term${countTerms.length>1?'s':''} (${sessionName})`;
WriteFile(pathCodeTextFile, addTxt);
// console.log('======== PDF GENERATION ENDS ================');
} else {
setCode = -1 * pdfList.length;
}
client.emit('query', {data: setData, title: setTitle, code: setCode, next: setNext, args: setArgs, view: JSON.stringify(setView)});
}
}
} catch (error) {
console.log('ERROR ON WATCHER: ', error);
}
}
if(!FileExists(pathJsonPdfList) && getResult !== null) {
PdfGenerator(getResult, wacthFiles);
}
// Watcher(pathWatchResults, setCode, wacthDir, 10000);
});
// }
}
}
} catch (error) {
})
client.on('disconnect', () => {
console.log('SERVER: Disconnected');
});
server.listen(portApi, () =>{
console.log('Server listens on port 8881')
});
// serve static files
app.use(express.static(pathPublic));
// [codes were removed here]
PdfGenerator.js
The problem lies in these functions: PdfGenerator & createPdf
'use strict';
process.setMaxListeners(Infinity) // fix for Puppeteer MaxListenerExceededWarning
const Puppeteer = require('puppeteer')
const {HtmlGenerator} = require('../components/HtmlGenerator')
const {WriteFile, FileExists, RandomNumber, RoundNumber, IsNumberFraction, ReadFile} = require('../components/Functions')
if (process.env.NODE_ENV !== 'production') {
require('dotenv').config();
}
const pathFirstTermResults = process.env.DIR_FIRST_TERM_RESULTS;
const pathSecondTermResults = process.env.DIR_SECOND_TERM_RESULTS;
const pathThirdTermResults = process.env.DIR_THIRD_TERM_RESULTS;
const publicDir = process.env.DIR_PUBLIC;
const cssFile = process.env.PATH_CSS_FILENAME;
const pathCssRaw = __dirname + '\\' + publicDir + '\\' + cssFile;
const pathCss = pathCssRaw.replace(`\\uploads`, '');
const tagCssReplace = process.env.TAG_CSS_REPLACE;
let jsonDir = process.env.PATH_JSON;
jsonDir = jsonDir.split('/').pop();
let htmlDir = process.env.DIR_HTML;
htmlDir = __dirname + '\\' + htmlDir.split('/').pop();
const htmlType1 = htmlDir + '\\' + process.env.HTML_TYPE1;
const htmlType2 = htmlDir + '\\' + process.env.HTML_TYPE2;
const htmlType3 = htmlDir + '\\' + process.env.HTML_TYPE3;
const pathJsonPdfList = './' + jsonDir + '/' + process.env.JSON_PDF_LIST_FILENAME;
const pathJsonPdfContent = __dirname + '\\' + jsonDir + '\\' + process.env.JSON_PDF_CONTENT;
const firstTermDir = 'first-term';
const secondTermDir = 'second-term';
const thirdTermDir = 'third-term';
let cumulativeFirstTermTotalList = {};
let cumulativeSecondTermTotalList = {};
let firstTermOnce = true;
let secondTermOnce = true;
let thirdTermOnce = true;
let isActive = false;
const getPath = (p, f) => {
let dir = pathFirstTermResults;
switch (p) {
case firstTermDir:
dir = pathFirstTermResults;
break;
case secondTermDir:
dir = pathSecondTermResults;
break;
case thirdTermDir:
dir = pathThirdTermResults;
break;
default:
break;
}
return dir + f
}
const resolution = {
x: 1920,
y: 1080
}
const args = [
'--disable-gpu',
`--window-size=${resolution.x},${resolution.y}`,
'--no-sandbox',
]
const createPdf = (page, content, templateType, filename, className, term, sessionName, isProcessActive, pdfFileList, cb) => {
let path, document, options;
path = getPath(term, filename);
if(path != null) {
let options = {
path: path,
format: 'A4',
printBackground: true,
margin: {
left: '0px',
top: '0px',
right: '0px',
bottom: '0px'
}
}
let templateData = '';
switch (templateType) {
case '1':
templateData = ReadFile(htmlType1);
break;
case '2':
templateData = ReadFile(htmlType2);
break;
case '3':
templateData = ReadFile(htmlType3);
break;
default:
templateData = ReadFile(htmlType1);
break;
}
(async() => {
const html = HtmlGenerator(content, templateData);
if(html != undefined && html !== '' && html != null) {
// create PDF file
cb(filename, className, term, sessionName, isProcessActive, pdfFileList);
// get style from .css & replace
const css = ReadFile(pathCss);
await page.setContent(html, { waitUntil: 'networkidle0'});
await page.addStyleTag(css);
await page.pdf(options);
page.close();
}
})()
}
}
const pdfGenerator = (json, cb) => {
let data = {};
let pdfFileList = [];
if(typeof json == 'string') {
data = JSON.parse(json)
} else {
data = json;
}
try {
// declare defaults
let filename = 'Student' + '.pdf';
let termName = firstTermDir;
const templateType = data.keys.templateType;
const session = data.classInfo.Session;
const sessionName = session.replace('/', '-');
const students = data.students;
const className = data.classInfo.Class_Name;
const recordFirstTerm = data.firstTerm;
const recordSecondTerm = data.secondTerm;
const recordThirdTerm = data.thirdTerm;
let pdfCreatedList = [];
let isReset = false;
let totalResultsExpected = Object.keys(recordFirstTerm).length + Object.keys(recordSecondTerm).length + Object.keys(recordThirdTerm).length;
let totalResultsCount = 0;
let jsonForPdf = {};
let record = {};
let sRecord, path, id, fName, lName;
// get each student
let logEndOnce = true;
let logBeforeOnce = true;
logBeforeOnce && console.log('============== *** ================');
logBeforeOnce && console.log('======== PDF GENERATION BEGINS ================');
const computeResult = (page, setTerm, setRecord, setReset) => {
const termName = setTerm;
const record = setRecord;
let isReset = setReset;
logBeforeOnce && console.log(`====== ${termName} RESULTS BEGINS ======`);
for(let elem of students){
id = elem.id;
fName = elem.firstName;
lName = elem.lastName;
filename = `${lName} ${fName} _${termName} ${sessionName}.pdf`;
// sRecord = record.filter(function (entry) { return entry[id] !== undefined; });
sRecord = record[id];
path = getPath(termName, filename);
// create pdf
if(!FileExists(path) && !FileExists(pathJsonPdfList)){
// generate final JSON for the student
// isReset = (pdfCreatedList.includes(id))? false: true;
jsonForPdf = finalJson(elem, sRecord, data, termName);
(pdfFileList.length < 1) && WriteFile(pathJsonPdfContent, JSON.stringify(jsonForPdf));
pdfFileList.push({
'term': termName,
'file': filename
});
totalResultsCount = pdfFileList.length;
const pdfDate = new Date();
console.log(`${filename} (${totalResultsCount}/${totalResultsExpected}) at ${pdfDate.getHours()}hr${pdfDate.getHours()>1?'s':''} - ${pdfDate.getMinutes()}min${pdfDate.getMinutes()>1?'s':''} - ${pdfDate.getSeconds()}sec${pdfDate.getSeconds()>1?'s':''}`);
isActive = (totalResultsExpected === totalResultsCount)? true: false;
logEndOnce = false;
// cb(filename, className, termName, sessionName, isActive, pdfFileList);
// WriteFile(path, null);
isReset = true;
createPdf(page, jsonForPdf, templateType, filename, className, termName, sessionName, isActive, pdfFileList, cb);
}
}
logBeforeOnce && console.log(`====== ${termName} RESULTS ENDS ======`);
}
// get each student result for First Term
const computeFirstTerm = (p) => {
return new Promise((resolve) => {
if(data.keys.firstTerm === '1') {
termName = firstTermDir;
record = recordFirstTerm;
pdfCreatedList = [];
isReset = false;
computeResult(p, termName, record, isReset)
}
resolve()
})
}
// get each student result for Second Term
const computeSecondTerm = (p) => {
return new Promise((resolve) => {
if(data.keys.secondTerm === '1') {
termName = secondTermDir;
record = recordSecondTerm;
pdfCreatedList = [];
isReset = false;
computeResult(p, termName, record, isReset)
}
resolve()
})
}
// get each student result for Third Term
const computeThirdTerm = (p) => {
return new Promise((resolve) => {
if(data.keys.thirdTerm === '1') {
termName = thirdTermDir;
record = recordThirdTerm;
pdfCreatedList = [];
isReset = false;
computeResult(p, termName, record, isReset)
}
resolve()
})
}
(async () => {
browser = await Puppeteer.launch({
headless: true,
handleSIGINT: false,
args: args,
});
const page = await browser.newPage();
await page.setViewport({
width: resolution.x,
height: resolution.y,
})
await computeFirstTerm(page);
await computeSecondTerm(page);
await computeThirdTerm(page);
browser.close()
})()
if(totalResultsExpected === totalResultsCount && totalResultsCount !== 0 && !logEndOnce) {
logEndOnce = true;
logBeforeOnce = false;
console.log('======== PDF GENERATION ENDS ================');
}
} catch (error) {
console.log('==== ERROR IN PDF GENERATION: ', error)
}
}
module.exports = {
PdfGenerator: pdfGenerator
}
ERROR
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
lerna ERR! yarn run start stderr:
<--- Last few GCs --->
[9884:000002D68A73C6B0] 1665171 ms: Scavenge 44.1 (45.8) -> 43.2 (45.8) MB, 223.9 / 0.0 ms (average mu = 0.956, current mu = 0.952) allocation failure
[9884:000002D68A73C6B0] 1684089 ms: Scavenge 44.1 (45.8) -> 43.3 (45.8) MB, 587.3 / 0.0 ms (average mu = 0.956, current mu = 0.952) allocation failure
[9884:000002D68A73C6B0] 1749901 ms: Scavenge 44.2 (45.8) -> 43.3 (45.8) MB, 5099.0 / 0.0 ms (average mu = 0.956, current mu = 0.952) allocation failure
<--- JS stacktrace --->
FATAL ERROR: Committing semi space failed. Allocation failed - JavaScript heap out of memory
1: 00007FF6ED61013F
2: 00007FF6ED59F396
3: 00007FF6ED5A024D
4: 00007FF6EDED19EE
5: 00007FF6EDEBBECD
6: 00007FF6EDD5F61C
7: 00007FF6EDD6933F
8: 00007FF6EDD5BF19
9: 00007FF6EDD5A0D0
10: 00007FF6EDD7EA06
11: 00007FF6EDAB1CD5
12: 00007FF6EDF5F3E1
13: 00007FF6EDF602E9
14: 000002D68C4EF69E
error Command failed with exit code 134.
Screenshot of Task Manager, Chromium running multiple instances of over 50.
I appreciate any help. I hope this can be resolved to give me a smooth PDF generation.
Thank you.
Example solution (limiting parallel browsers)
I created you a PdfPrinter class which you can integrate into your setup. It allows you to limit the amount of parallel pdf generation jobs and allows setting a limit and manages opening/closing the browser for you. The PdfPrinter class is also highly coupled and needed some modification for using it as a general queue. Logicwise this can be modified to be a general queue.
You can try to integrate that into your code. This is a fully working test example with simplified pdfs (without the part of getting the actual data from the excel..)
As far as I understood your code, you do not need to pass the page around all your functions. First create your html + css and then use the pdfPrinter and let it handle page creation + browser launching..
(I like to code stuff like this so I went straight ahead..)
var puppeteer = require('puppeteer')
const defaultPrinterOptions = {
format: 'A4',
printBackground: true,
margin: {
left: '0px',
top: '0px',
right: '0px',
bottom: '0px'
}
}
class PdfPrinter {
maxBrowsers = 2
enqueuedPrintJobs = []
failedJobs = []
browserInstances = 0
// max browser instances in parallel
constructor(maxBrowsers) {
this.maxBrowsers = maxBrowsers
}
/**
*
* #param {*} html the html content to print
* #param {*} css to apply to the page
* #param {*} printOptions options passed to puppeteer
*/
// enqueues a print but the exact end moment cannot be known..
enqueuePrint = (html, css, path, done) => {
// merge custom options with defaultOptions..
const printOptions = {
...defaultPrinterOptions,
// add the path to the options.
path: path
}
// create a function which can be stored in an array
// it will later be grabbed by startPrinter() OR at the time any
// brwoser freed up..
// the function needs to be passed the actual used browser instance!
this.enqueuedPrintJobs.push(async(browser) => {
// catch the error which may be produced when printing something..
try {
// print the document
await this.print(browser, html, css, printOptions)
} catch (err) {
console.error('error when printing document..CLosing browser and starting a new job!!', printOptions.path)
console.error(err)
// store someting so you now what failed and coudl be retried or something..
this.failedJobs.push({ html, css, path: printOptions.path })
// puppeteer can run into erros too!!
// so close the browser and launch a new one!
await this.closeBrowser(browser)
browser = await this.launchBrowser()
}
// after the print, call done() so the promise is resovled in the right moment when
// this particular print has ended.!
done()
// start the next job right now if there are any left.
const job = this.enqueuedPrintJobs.shift()
if (!job) {
console.log('No print jobs available anymore. CLosing this browser instance.. Remaining browsers now:', this.maxBrowsers - this.browserInstances + 1)
await this.closeBrowser(browser)
return
}
// job is actually this function itself! It will be executed
// and automatically grab a new job after completion :)
// we pass the same browser instance to the next job!.
await job(browser)
})
// whenever a print job added make sure to start the printer
// this starts new browser instances if the limit is not exceeded resp. if no browser is instantiated yet,
// and does nothing if maximum browser count is reached..
this.tryStartPrinter()
}
// same as enqueuePrint except it wraps it in a promise so we can now the
// exact end moment and await it..
enqueuePrintPromise(html, css, path) {
return new Promise((resolve, reject) => {
try {
this.enqueuePrint(html, css, path, resolve)
} catch (err) {
console.error('unexpected error when setting up print job..', err)
reject(err)
}
})
}
// If browser instance limit is not reached will isntantiate a new one and run a print job with it.
// a print job will automatically grab a next job with the created browser if there are any left.
tryStartPrinter = async() => {
// Max browser count in use OR no jobs left.
if (this.browserInstances >= this.maxBrowsers || this.enqueuedPrintJobs.length === 0) {
return
}
// browser instances available!
// create a new one
console.log('launching new browser. Available after launch:', this.maxBrowsers - this.browserInstances - 1)
const browser = await this.launchBrowser()
// run job
const job = this.enqueuedPrintJobs.shift()
await job(browser)
}
closeBrowser = async(browser) => {
// decrement browsers in use!
// important to call before closing browser!!
this.browserInstances--
await browser.close()
}
launchBrowser = async() => {
// increment browsers in use!
// important to increase before actualy launching (async stuff..)
this.browserInstances++
// this code you have to adjust according your enviromnemt..
const browser = await puppeteer.launch({ headless: true })
return browser
}
// The actual print function which creates a pdf.
print = async(browser, html, css, printOptions) => {
console.log('Converting page to pdf. path:', printOptions.path)
// Run pdf creation in seperate page.
const page = await browser.newPage()
await page.setContent(html, { waitUntil: 'networkidle0' });
await page.addStyleTag({ content: css });
await page.pdf(printOptions);
await page.close();
}
}
// testing the PDFPrinter with some jobs.
// make sure to run the printer in an `async` function so u can
// use await...
const testPrinterQueue = async() => {
// config
const maxOpenedBrowsers = 5 // amount of browser instances which are allowed to be opened in parallel
const testJobCount = 100 // amount of test pdf jobs to be created
const destDir = 'C:\\somepath' // the directory to store the pdfs in..
// create sample jobs for testing...
const jobs = []
for (let i = 0; i < testJobCount; i++) {
jobs.push({
html: `<h1>job number [${i}]</h1>`,
css: 'h1 { background-color: red; }',
path: require('path').join(destDir, `pdf_${i}.pdf`)
})
}
// track time
const label = 'printed a total of ' + testJobCount + ' pdfs!'
console.time(label)
// run the actual pdf generation..
const printer = new PdfPrinter(maxOpenedBrowsers)
const jobProms = []
for (let job of jobs) {
// run jobs in parallel. Each job wil be runned async and return a Promise therefor
jobProms.push(
printer.enqueuePrintPromise(job.html, job.css, job.path)
)
}
console.log('All jobs enqueued!! Wating for finish now.')
// helper function which awaits all the print jobs, resp. an array of promises.
await Promise.all(jobProms)
console.timeEnd(label)
// failed jobs::
console.log('jobs failed:', printer.failedJobs)
// as file:
await require('fs').promises.writeFile('failed-jobs.json', JSON.stringify(printer.failedJobs))
}
testPrinterQueue().then(() => {
console.log('done with everyting..')
}).catch(err => {
console.error('unexpected error occured while printing all pages...', err)
})
You only need to adjust the destDir / openedBrowsers and testJobCount vars in the beginning of testPrinterQueue() for getting this to work.
What caused the problem in your code
Let's have a look at this piece
(async () => {
browser = await Puppeteer.launch({
headless: true,
handleSIGINT: false,
args: args,
});
const page = await browser.newPage();
await page.setViewport({
width: resolution.x,
height: resolution.y,
})
await computeFirstTerm(page);
await computeSecondTerm(page);
await computeThirdTerm(page);
browser.close()
})()
You created an anonymous function which is executed immediatly. Within the function all the statements are correctly awaited using await. But if you run this whole piece within a synchronious part of your application, the whole function will start immediatly but NOT been awaited before running next code.
Checkout this example:
//utility
function wait(ms) {
return new Promise(resolve => {
setTimeout(resolve, ms)
})
}
const AsyncFunction = async() => {
console.log('Async named function started')
// simulate execution time of 2 seconds
await wait(2000)
console.log('Async named function ended')
};
function SyncFunction() {
console.log('sync function started')
// example of async function execution within a sync function..
AsyncFunction();
// what you have done in your code:
(async() => {
console.log('Async anonymus function started')
await wait(3000)
console.log('Async anonymus function ended')
})()
// what
console.log('sync function ended.')
}
SyncFunction()
console.log('done')
Note the output:
Async named function started
Async anonymus function started
sync function ended. // => sync function already ended
done // sync function ended and code continues execution.
Async named function ended
Async anonymus function ended
To correctly await your async stuff you need to put your whole application in async scope:
//utility
function wait(ms) {
return new Promise(resolve => {
setTimeout(resolve, ms)
})
}
const AsyncFunction = async() => {
console.log('Async named function started')
// simulate execution time of 2 seconds
await wait(2000)
console.log('Async named function ended')
};
// this is now async!!
async function SyncFunction() {
console.log('sync function started')
// example of async function execution within a sync function..
await AsyncFunction();
// what you have done in your code:
await (async() => {
console.log('Async anonymus function started')
await wait(3000)
console.log('Async anonymus function ended')
})()
// what
console.log('sync function ended.')
}
SyncFunction().then(() => {
console.log('done')
}).catch(err => {
console.error('unexpected error occured..')
})
This output is what we want
sync function started
Async named function started
Async named function ended
Async anonymus function started
Async anonymus function ended
sync function ended.
done
Hope this helps you understand.
Feel free to leave a comment.
I have a loop inside my async function which essentially is meant to solve captchas, however the awaits within the loop don't seem to be working...
Here is what the loop looks like:
for(var i=0; i < 7; i++){
fileName = `./tasks/myfile-${i.toString()}.json`
// SOLVE reCAPTCHAs
const requestId = await initiateCaptchaRequest(apiKey);
const response = await pollForRequestResults(apiKey, requestId);
console.log(`SOLVED CAPTCHA - ${response}`);
// Should run this function AFTER the response has been received
await enter(response);
}
And here is what the functions look like that the loop utilises to solve the captcha (code from: https://medium.com/#jsoverson/bypassing-captchas-with-headless-chrome-93f294518337):
async function initiateCaptchaRequest(apiKey) {
const formData = {
method: 'userrecaptcha',
googlekey: siteDetails.sitekey,
key: apiKey,
pageurl: siteDetails.pageurl,
json: 1
};
const response = await request.post('http://2captcha.com/in.php', {form: formData});
return JSON.parse(response).request;
}
async function pollForRequestResults(key, id, retries = 30, interval = 1500, delay = 15000) {
await timeout(delay);
return poll({
taskFn: requestCaptchaResults(key, id),
interval,
retries
});
}
function requestCaptchaResults(apiKey, requestId) {
const url = `http://2captcha.com/res.php?key=${apiKey}&action=get&id=${requestId}&json=1`;
return async function() {
return new Promise(async function(resolve, reject){
const rawResponse = await request.get(url);
const resp = JSON.parse(rawResponse);
if (resp.status === 0) return reject(resp.request);
resolve(resp.request);
});
}
}
const timeout = millis => new Promise(resolve => setTimeout(resolve, millis))
My problem is that the loop seen above should run the initiateCaptchaRequest function which gets the requestId, THEN run the pollForRequestResults function to get the response and THEN run the enter function.
But right now the awaits don't seem to be working and almost instantly after the initiateCaptchaRequest function is run, the pollForRequestResults function runs which returns a JSON parse error obviously because the requestId has not been gathered yet, and is used in the requestCaptchaResults function...
Any help is appreciated!
I tried to recreate your issue, but it seem to work perfectly fine for me. But I think the issue is in requestCaptchaResults function
(async ()=>{
for(var i=0; i < 7; i++){
await initiateCaptchaRequest(i);
console.log(i)
}
})()
function initiateCaptchaRequest(i){
console.log('sdas'+i);
return new Promise((resolve, reject)=>{
setTimeout(()=>{resolve();}, 4000);
});
}
output:
sdas0
0
sdas1
1
sdas2
2
sdas3
3
sdas4
4
sdas5
5
sdas6
6
await is not works in for loop because for loop is not async
so you have to make for loop to promise
const newFunc = ()=>{
return new Promise(async (resolve,reject)=>{
// SOLVE reCAPTCHAs
const requestId = await initiateCaptchaRequest(apiKey);
const response = await pollForRequestResults(apiKey, requestId);
console.log(`SOLVED CAPTCHA - ${response}`);
// Should run this function AFTER the response has been received
const data = await enter(response);
resolve(data);
})
}
Yourfunction(){
val = []
for(var i=0; i < 7; i++){
fileName = `./tasks/myfile-${i.toString()}.json`
val.push(**your arguments)
}
return new Promise.all(val).then((res)=>{return res;}).catch((err)=> {return err;})
}
I want my function to execute X(=3) times until success.
In my situation I'm running kinesis.putRecord (from AWS API), and if it fails - I want to run it again until it succeeds, but not more than 3 tries.
I'm new to NodeJS, and the code I wrote smells bad.
const putRecordsPromise = function(params){
return new Promise((resolve, reject) => {
kinesis.putRecord(params, function (err, data) {
resolve(err)
});
})
}
async function waterfall(params){
try{
let triesCounter = 0;
while(triesCounter < 2){
console.log(`try #${triesCounter}`)
let recordsAnswer = await putRecordsPromise(params)
if(!recordsAnswer){
console.log("success")
break;
}
triesCounter += 1;
}
// continue ...
} catch(err){
console.error(err)
}
}
waterfall(params)
I promise the err result. Afterwards, If the err is empty, then all good. otherwise, continue running the same command.
I'm sure there is a smarter way to do this. Any help would be appreciated.
I think, all the Aws functions can return a Promise out of the box, then you can just put the call into try/catch:
let triesCounter = 0;
while(triesCounter < 2){
console.log(`try #${triesCounter}`)
try {
await kinesis.putRecord(params).promise();
break; // 'return' would work here as well
} catch (err) {
console.log(err);
}
triesCounter ++;
}
In functional style:
...
await tryUntilSucceed(() => kinesis.putRecord(params).promise());
...
async function tryUntilSucceed(promiseFn, maxTries=3) {
try {
return await promiseFn();
} catch (e) {
if (maxTries > 0) {
return tryUntilSucceed(promiseFn, maxTries - 1);
}
throw e;
}
}
Make a little module, say try-and-try-again.js:
exports = module.exports = tryAndTryAgain;
function tryAndTryAgain( maxTries, thisContext , fn, ...argv) {
let success = false;
for (let i = i ; i < maxTries && !success ; ++i ) {
let rc = fn.apply(thisContext, args);
success = rc == 0 ? true : false;
}
return success;
}
Then you can use it anywhere:
const tryAndTryAgain = require('./try-and-try-again');
function somethingThatMightNeedARetry() { ... }
const succeeded = tryAndTryAgain( 3 , null, somethingThatMightNeedARetry, 'arg-1', 'arg-2', 'arg-3' );
There is an npm package called async-retry that is pretty handy. It acts as a wrapper for your function and retries if anything throws (with some exceptions that you can handle, see their example below).
// Packages
const retry = require('async-retry')
const fetch = require('node-fetch')
await retry(async bail => {
// if anything throws, we retry
const res = await fetch('https://google.com')
if (403 === res.status) {
// don't retry upon 403
bail(new Error('Unauthorized'))
return
}
const data = await res.text()
return data.substr(0, 500)
}, {
retries: 5
})
It is 2016, Node has had nearly full ES6 support since v4, and Promises have been around since 0.12. It's time to leave callbacks in the dust IMO.
I'm working on a commander.js-based CLI util which leverages a lot of async operations - http requests and user input. I want to wrap the Commander actions in async functions so that they can be treated as promises, and also to support generators (useful for the co-prompt library I'm using for user input).
I've tried wrapping the CB with co in two ways:
1)
program.command('myCmd')
.action(program => co(function* (program) {...})
.catch(err => console.log(err.stack)) );
and
2) program.command('myCmd').action(co.wrap(function* (program) { .. }));
The problem with 1) is that the program parameter isn't passed
The problem with 2) is that errors are swallowed...
I'd really like to get this working as it yields much nicer code in my use case - involving a lot of http requests and also waiting for user input using the co-prompt library..
Is it a better option altogether perhaps to wrap program.Command.prototype.action somehow?
thanks!
I've used a bespoke version of something like co to get a db.exec function which uses yield to do database request. You can pass parameters into a generator function (I pass in a connection object - see the comment where I do it).
Here is by db.exec function that is very similar to what co does
exec(generator) {
var self = this;
var it;
debug('In db.exec iterator');
return new Promise((accept,reject) => {
debug('In db.exec Promise');
var myConnection;
var onResult = lastPromiseResult => {
debug('In db.exec onResult');
var obj = it.next(lastPromiseResult);
if (!obj.done) {
debug('db.exec Iterator NOT done yet');
obj.value.then(onResult,reject);
} else {
if (myConnection) {
myConnection.release();
debug('db.exec released connection');
}
accept(obj.value);
debug('db.exec Promise Resolved with value %d',obj.value);
}
};
self._connection().then(connection => {
debug('db.exec got a connection');
myConnection = connection;
it = generator(connection); //This passes it into the generator
onResult(); //starts the generator
}).catch(error => {
logger('database', 'Exec Function Error: ' + error.message);
reject(error);
});
});
}
the connection object also wraps by database connection object and provides a generator function ability to process the rows of the results from the database, but I won't post that here (although the example below is using it to process the rows).
Here is an example of using the exec function to run a sequence of sql
db.exec(function*(connection) {
if (params.name === ADMIN_USER) {
debug('Admin Logon');
user.name = ADMIN_DISPLAY;
user.keys = 'A';
user.uid = 0;
let sql = 'SELECT passwordsalt FROM Admin WHERE AdminID = 0';
connection.request(sql);
yield connection.execSql(function*() {
let row = yield;
if (row) {
user.nopass = (row[0].value === null);
} else {
user.nopass = false;
}
debug('Admin Password bypass ' + user.nopass.toString());
});
} else {
debug('Normal User Logon');
let sql = `SELECT u.UserID,PasswordSalt,DisplayName,AccessKey,l.LogID FROM Users u
LEFT JOIN UserLog l ON u.userID = l.userID AND DATEDIFF(D,l.LogDate,GETDATE()) = 0
WHERE u.UserName = #username`;
let request = connection.request(sql);
request.addParameter('username',db.TYPES.NVarChar,params.name);
let count = yield connection.execSql(function*() {
let row = yield;
if (row) {
user.uid = row[0].value;
user.name = row[2].value;
user.keys = (row[3].value === null) ? '' : row[3].value;
user.nopass = (row[1].value === null) ;
user.lid = (row[4].value === null) ? 0 : row[4].value;
debug('Found User with uid = %d and lid = %d, keys = %s',
user.uid, user.lid, user.keys);
}
});
if (count === 0) {
debug('Not Found User');
// couldn't find name in database
reply(false,false);
return;
}
}
if (!user.nopass) {
debug('Need a Password');
//user has a password so we must check it
passGood = false; //assume false as we go into this
let request = connection.request('CheckPassword');
request.addParameter('UserID',db.TYPES.Int,user.uid);
request.addParameter('password',db.TYPES.VarChar,params.password);
yield connection.callProcedure(function*() {
let row = yield;
if (row) {
//got a valid row means we have a valid password
passGood = true;
}
});
} else {
passGood = true;
}
if (!passGood) {
debug('Not a Good Pasword');
reply(false,true);
} else {
if (user.uid !== 0 && user.lid === 0) {
let sql = `INSERT INTO UserLog(UserID,LogDate,TimeOn,UserName) OUTPUT INSERTED.logID
VALUES(#uid,GETDATE(),GETDATE(),#username)`;
let request = connection.request(sql);
request.addParameter('uid',db.TYPES.Int,user.uid);
request.addParameter('username',db.TYPES.NVarChar,user.name);
yield connection.execSql(function*() {
let row = yield;
if (row) {
user.lid = row[0].value;
debug('Users Log Entry = %d',user.lid);
}
});
}
reply(true,user);
}
})
.catch((err) => {
logger('database','Error on logon: ' + err.message);
reply(false,false);
});
});
There is a quite simple way to do async function in Commander.js
async function run() {
/* code goes here */
}
program
.command('gettime')
.action(run);
program.parse(process.argv);