hi how can I break out of the for loop ? I want to be able to break out of it in the callback in the if statement
I want this program to create a folder in the given directory and every time it throws an error I want it to change the folder name and add a number to it so when it says that the folder already exists, It'll create a unique folder name until it doesn't throw an error.
I will check for the error code later help me solve this first
const path = require('path');
function folder(folderName) {
for (let i = 1; i <= 10; i++) {
let pathNumber = i;
let fullPath = folderName + pathNumber;
fs.mkdir(path.join("D:", fullPath), (err) => {
if (!err) {
return; // I want to break out of the loop here
}
})
}
}
folder("folder");
You can't write the code that way because the for loop will already be done before any of the fs.mkdir() callbacks are called. They are asynchronous and happen LATER.
If you want to execute one iteration of the loop, including the fs.mkdir() before moving on to any other, then you can use async/await with fs.promises.mkdir().
Here's what a solution could look like with fs.promises.mkdir(). I've also added error handling for the case where all 10 sub-dir names you're trying already exist.
async function folder(folderName) {
let lastError;
for (let pathNumber = 1; pathNumber <= 10; pathNumber++) {
let fullPath = path.join("D:", folderName + pathNumber);
try {
await fs.promises.mkdir(fullPath);
return fullPath;
} catch(e) {
lastError = e;
// ignore error so we keep trying other numbers
}
}
throw lastError;
}
folder("folder").then(fullPath => {
console.log(`dir created: ${fullPath}`);
}).catch(err => {
console.log(err);
});
Much simpler without await
const numFolders = 10,
folders = Array.from(Array(numFolders), (_,i) => `folder${i+1}`), len = folder.length;
let cnt = 0;
const makeFolder = () => {
if (cnt >= len) return; // stop because done
fs.mkdir(path.join("D:", fullPath), (err) => {
if (err) {
makeFolder(); // only call again if error
}
cnt++
}
makeFolder()
Related
I am writing a test case which requires me to reload the page N number of times, and compare its title for a value, if that value does not exists then break the while loop without rising error.
Below is a demo program, similar to the one that I am looking to implement.
/// <reference types='cypress' />
it("Visiting Google",function(){
var webUrl = 'https://html5test.com/'
cy.visit(webUrl)
var loop_iter = 0
while(loop_iter < 5)
{
cy.get('body:nth-child(2) div:nth-child(2) div.header h1:nth-child(1) > em:nth-child(2)').then(($text_data) =>{
if($text_data.text().contains('HTML123'))
{
cy.log(" --> ITERATION = ",loop_iter)
cy.reload()
}
else
{
cy.log("Unknown website")
loop_iter = 10
}
})
loop_iter += 1
}
})
I need a way to break from the while loop when the else part is executed, without rising any error.
The if condition when false returns AssertionError, in such case it should execute else part.
cy.title() is asynchronous (proof is, you need to use .then()), so, the entire while loop ends even before the first .then() triggers. That's how asynchronism works.
You need another approach :
it("Visiting Google", async function () {
var webUrl = 'https://html5test.com/'
cy.visit(webUrl)
for (let i = 0; i < 5; i++) { // You can't await in a 'while' loop
const $text_data = await cy.title();
if ($text_data.includes('HTML')) {
cy.log(" --> ITERATION = ", i)
cy.reload()
}
else {
cy.log("Unknown website")
break;
}
}
})
Please take a look at the sample recipe Page reloads. It uses recursion as suggested in comments.
This is your code adapted to the pattern,
it('reload until "HTML" disappears', () => {
// our utility function
const checkAndReload = (recurse_level = 0) => {
cy.title().then(title => {
if (title.includes('HTML') && recurse_level < 5) {
cy.log(" --> ITERATION = ", recurse_level)
cy.wait(500, { log: false }) // just breathe here
cy.reload() // reload
checkAndReload(recurse_level + 1) // check again
} else {
cy.log("Unknown website")
}
})
}
cy.visit('https://html5test.com/') // start the test by visiting the page
checkAndReload() // and kicking off the first check
})
consider this scenario:
I have 2 csv files, each one is sorted and contains the id filed.
I need to join the rows using the id field. Because the files are already sorted by the id I wanted to perform merge join (https://en.wikipedia.org/wiki/Sort-merge_join).
For that I need to have a way to load some portion of both files, process it and iteratively load more again from one or both files.
(The files are big and would not fit into memory so only streaming approach will work).
The problem is the Node API, what to use? readline will not work because of https://github.com/nodejs/node/issues/33463. Any other ideas?
I had to do something quite similar recently and decided to use the node-line-reader module that has a simpler interface than the built-in readline. I then created a little recursive function that determines which file to read from next by comparing the id of each csv-entry of each provided file. After that the corresponding line gets written out to the target file, and the method is called again until all lines of all files are processed. Here's the whole class I ended up with:
const fs = require('fs');
const LineReader = require('node-line-reader').LineReader;
class OrderedCsvFileMerger {
constructor(files, targetFile) {
this.lineBuffer = [];
this.initReaders(files);
this.initWriter(targetFile);
}
initReaders(files) {
this.readers = files.map(file => new LineReader(file));
}
initWriter(targetFile) {
this.writer = fs.createWriteStream(targetFile);
}
async mergeFiles() {
// initially read first line from all files
for (const reader of this.readers) {
this.lineBuffer.push(await this.nextLine(reader));
}
return this.merge();
}
async nextLine(reader) {
return new Promise((resolve, reject) => {
reader.nextLine(function (err, line) {
if (err) reject(err);
resolve(line);
});
})
}
async merge() {
if (this.allLinesProcessed()) {
return;
}
let currentBufferIndex = -1;
let minRowId = Number.MAX_VALUE;
for (let i = 0; i < this.lineBuffer.length; i++) {
const currentRowId = parseInt(this.lineBuffer[i]); // implement parsing logic if your lines do not start
// with an integer id
if (currentRowId < minRowId) {
minRowId = currentRowId;
currentBufferIndex = i;
}
}
const line = this.lineBuffer[currentBufferIndex];
this.writer.write(line + "\n");
this.lineBuffer[currentBufferIndex] = await this.nextLine(this.readers[currentBufferIndex]);
return this.merge();
}
allLinesProcessed() {
return this.lineBuffer.every(l => !l);
}
}
(async () => {
const input = ['./path/to/csv1.csv', './path/to/csv2.csv'];
const target = './path/to/target.csv';
const merger = new OrderedCsvFileMerger(files, output);
await merger.mergeFiles();
console.log("Files were merged successfully!")
})().catch(err => {
console.log(err);
});
I am trying to get a custom action running to simply incrementing a value on passing a specific node on the flow.
My custom actions looks like this:
function action(bp: typeof sdk, event: sdk.IO.IncomingEvent, args: any, { user, temp, session } = event.state) {
/** Your code starts below */
let i = undefined
const p = new Promise((resolve, reject) => {
if (i === undefined) {
resolve((i = 0))
} else if (i >= 0) {
resolve(i + 1)
} else {
reject('i cannot be < 0')
}
})
const runCount = async () => {
try {
const counter = await p
i = counter
return (session.count = counter)
} catch (err) {
console.log(err)
}
}
return runCount()
/** Your code ends here */
}
When I runCount() variable i will be set to 0. But then, after in rerun runCount() it does not increment further.
What do I need to do to save the variable so it increments on every runCount() call.
Greetings
Lorenz
I just managed to solve the problem.
I had to declare i = session.count at the beginning.
Now it gets the value out of the session state and increments the state on every call.
Maybe someone gets some help out of this.
Lorenz
I've been scouring similar problems but haven't seem to have found a solution that quite works on my end. So I'm working on a Discord bot that takes data from a MongoDB database and displays said data in the form of a discord embedded message using Mongoose. For the most part, everything is working fine, however one little section of my code is giving me trouble.
So I need to import an array of both all available users and the "time" data of each of those users. Here is the block of code I use to import said data:
for (i = 0;i < totalObj; i++){
timeArray[i] = await getData('time', i);
userArray[i] = await getData('user', i);
}
Now this for loop references a function I made called getData which obtains the data from MongoDB by this method:
async function getData(field, value){
var data;
await stats.find({}, function(err, result){
if(err){
result.send(err);
}else{
data = result[value];
}
});
if(field == "user"){
return data.user;
}else if (field == "time"){
return data.time;
}else{
return 0;
}
So that for loop is where my errors currently lie. When I try to run this code and display my data through a discord message, I get this error and the message does not get sent:
(node:13936) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'time' of undefined
Now the strange thing is, this error does not happen every time. If I continue calling the command that triggers this code from my discord server, it's almost like a 50/50 shot if the command actually shows the message or instead gives this error. It is very inconsistent.
This error is confounding me, as the undefined part does not make sense to me. The objects that are being searched for in the mongoDB collection are definitely defined, and the for loop never exceeds the number of objects present. My only conclusion is that I'm doing something wrong with my asynchronous function design. I have tried altering code to use the getData function less often, or to not use awaits or asynchronous design at all, however this leaves my final discord message with several undefined variables and an eventual crash.
If anyone has any advice or suggestions, that would be very much appreciated. Just for reference, here is the full function that receives the data, sorts it, and prepares a string to be displayed on the discord server (though the error only seems to occur in the first for loop):
async function buildString(){
var string = "";
var totalObj;
var timeArray = [];
var userArray = [];
var stopSort = false;
await stats.find({}, function(err, result){
if(err){
result.send(err);
}else{
totalObj = result.length;
}
});
for (i = 0;i < totalObj; i++){
timeArray[i] = await getData('time', i);
userArray[i] = await getData('user', i);
}
while(!stopSort){
var keepSorting = false;
for(i = 0; i < totalObj ; i++){
var target = await convertTime(timeArray[i]);
for(j = i + 1 ; j < totalObj ; j++){
var comparison = await convertTime(timeArray[j]);
if(target > comparison){
//Switch target time with comparison time so that the lower time is up front
var temp = timeArray[i];
timeArray[i] = timeArray[j];
timeArray[j] = temp;
//Then switch the users around so that the user always corresponds with their time
var userTemp = userArray[i];
userArray[i] = userArray[j];
userArray[j] = userTemp;
//The loop will continue if even a single switch is made
keepSorting = true;
}
}
}
if(!keepSorting){
stopSort = true;
}
}
//String building starts here
var placeArray = [':first_place: **1st', ':second_place: **2nd', ':third_place: **3rd', '**4th', '**5th', '**6th', '**7th', '**8th', '**9th', '**10th'];
for(i = 0; i < totalObj; i++){
string = await string.concat(placeArray[i] + ": " + userArray[i] + "** - " + timeArray[i] + " \n\n");
console.log('butt');
}
console.log("This String:" + string);
return string;
}
I think problem is you are trying to await function with callback, it will not work => access to data.time may run before data = result[value]. If you need await callback, you can use custom Promise (or use util.promisify, more info here)
Promise:
function findStats(options) {
return new Promise((resolve, reject) => {
return stats.find(options, function (err, result) {
if (err) {
return reject(err)
}
return resolve(result)
})
})
}
utils.promisify
const util = require('util');
const findStats = util.promisify(stats.find);
Now you can use await in your function
async function getData(field, value) {
try {
const result = await findStats({})
const data = result.value
if (field === 'user') {
return data.user
}
if (field === 'time') {
return data.time
}
return 0
} catch (error) {
// here process error the way you like
// or remove try-catch block and sanitize error in your wrap function
}
}
I'm writing an Electron program which takes a CSV file as input, and does file operations depending on the CSV content and file existence (it's to manage MAME arcade roms).
In order to have a progress bar on the UI side, I have switched the code from fully synchronous (because it was much easier) to asynchronous.
I just cannot find out how to reliably display a message to the user when all the lines in the CSV file are processed, and all the zip files are copied or removed.
Here is a (simplified) sample method:
fs.readFile(file, { 'encoding': 'utf8' }, (err, fileContents) => {
let fileCsv = csvparse(fileContents);
let lines = fileCsv.length;
fileCsv.forEach((line) => {
lines--;
let zip = line.name + '.zip';
let sourceRom = path.join(romset, zip);
let destRom = path.join(selection, zip);
this.emit('progress.add', fileCsv.length, fileCsv.length - lines, zip);
if (fs.existsSync(sourceRom) && !fs.existsSync(destRom)) {
fs.copy(sourceRom, destRom, (err) => {
let sourceChd = path.join(romset, game);
if (fs.existsSync(sourceChd)) {
fs.copy(sourceChd, path.join(selection, game), (err) => {
if (lines <= 0) { callback(); } // chd is copied
});
} else {
if (lines <= 0) { callback(); } // no chd, rom is copied
}
});
} else {
if (lines <= 0) { callback(); } // no source found or already exists
}
});
});
The problem is that the CSV file is processed really fast, but the file are not copied as fast. So it decrements the lines counter to 0, then after each file copy, it finds that it's zero and triggers the callback.
How do I reliably trigger the callback at the end of all these nested callbacks and conditions?
Thanks
I tried to change the code without massively overwriting your style - assuming there is a reason to avoid things like bluebird, async/await & native Promises, and the async lib.
You need to decrement lines after a line is processed. I pulled the processing logic out into a function to make this clearer:
function processLine({
sourceRom, destRom, romset, game, callback
}) {
if (fs.existsSync(sourceRom) && !fs.existsSync(destRom)) {
fs.copy(sourceRom, destRom, (err) => {
// *really* should handle this error
let sourceChd = path.join(romset, game);
if (fs.existsSync(sourceChd)) {
fs.copy(sourceChd, path.join(selection, game), (err) => {
// *really* should handle this error
callback();
});
} else {
callback();
}
});
} else {
callback() // no source found or already exists
}
}
fs.readFile(file, { 'encoding': 'utf8' }, (err, fileContents) => {
let fileCsv = csvparse(fileContents);
let lines = fileCsv.length;
fileCsv.forEach((line) => {
let zip = line.name + '.zip';
let sourceRom = path.join(romset, zip);
let destRom = path.join(selection, zip);
this.emit('progress.add', fileCsv.length, fileCsv.length - lines, zip);
processLine({ sourceRom, destRom, game, romset, callback: () => {
lines--;
if (lines <= 0) {
callback();
}
}})
});
});