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Why am I intermittently writing partial arrays to files in Node with fs.readFileSync?

Context
I'm retrieving data from the ESPN API to fetch weekly NFL matchup data. So, I'm making 18 api calls each time I need to fetch this data to account for all 18 weeks in the NFL season. I'm then creating an array with the data I need from the responses to those calls and writing out 18 files that align with each week in the NFL season (week1.json, week2.json, etc.).
Problem
The problem is that when I call my endpoint, I am seeing 2 things intermittently, and not necessarily at the same time:
(1) Some of the json files(week1.json, week2.json, etc.) include only a portion of the expected array. So, instead of 16 objects in the array, I may see only 4, or only 6, etc. Why would I only see a portion of the response data written to the array that's ultimately written to the .json files?
(2) Not all files are written to each time the endpoint is called. So, I may see that only week1-week5's .json files are written. Why aren't all of them updated?
Problem Code
// iterate 18 times
for (let i = 0; i < 18; i++) {
let weekNumber;
weekNumber = i + 1;
const week = fs.readFileSync(`./pickem/week${weekNumber}.json`, 'utf8');
const weekJson = JSON.parse(week);
// empty weekJson.games array
weekJson.games = []
// get all items
axios.get(`https://sports.core.api.espn.com/v2/sports/football/leagues/nfl/seasons/2022/types/2/weeks/${weekNumber}/events?lang=en&region=us`)
.then(response => {
const schedule = [];
// get all items from response
const items = response.data.items
// console.log(response.data.items)
items.forEach(item => {
// make get call to $ref
axios.get(item.$ref)
.then(response => {
// get name
const name = response.data.name
// get date
const date = response.data.date
// get event id
const eventid = response.data.id
// get team ids
let team1 = response.data.competitions[0].competitors[0].id
let team2 = response.data.competitions[0].competitors[1].id
// create new object
const newObject = {
name: name,
date: date,
eventid: eventid,
team1: team1,
team2: team2
}
// add games for week
weekJson.games.push(newObject);
fs.writeFileSync(`./pickem/week${weekNumber}.json`, JSON.stringify(weekJson));
})
.catch(error => {
console.log(error)
})
})
}).catch(error => {
console.log(error)
})
}
Updated Code
router.get('/getschedules', (req, res) => {
async function writeGames() {
// iterate 18 times
for (let i = 0; i < 18; i++) {
let weekNumber;
weekNumber = i + 1;
const week = fs.readFileSync(`./pickem/week${weekNumber}.json`, 'utf8');
const weekJson = JSON.parse(week);
// empty weekJson.games array
weekJson.games = []
// get all items
// Add await keyword to wait for a week to be processed before going to the next one
await axios.get(`https://sports.core.api.espn.com/v2/sports/football/leagues/nfl/seasons/2022/types/2/weeks/${weekNumber}/events?lang=en&region=us`)
.then(async (response) => { // add async to be able to use await
const schedule = [];
// get all items from response
const items = response.data.items
console.log(response.data.items)
// Use standard loop to be able to benefit from async/await
for (let item of items) {
// make get call to $ref
// wait for an item to be processed before going to the next one
await axios.get(item.$ref)
.then(response => {
// get name
const name = response.data.name
// get date
const date = response.data.date
// get event id
const eventid = response.data.id
// get team ids
let team1 = response.data.competitions[0].competitors[0].id
let team2 = response.data.competitions[0].competitors[1].id
// create new object
const newObject = {
name: name,
date: date,
eventid: eventid,
team1: team1,
team2: team2
}
// add games for week
weekJson.games.push(newObject);
})
.catch(error => {
console.log(error)
})
}
// moved out of the for loop since you only need to write this once
fs.writeFileSync(`./pickem/week${weekNumber}.json`, JSON.stringify(weekJson));
}).catch(error => {
console.log(error)
})
}
}
writeGames();
})

Your issue might come from the fact that you are looping over an array of item that triggers parallel asynchronous calls and write weekJson before you get the entire data. (But theoretically your code should work if writeSyncFile is really synchronous, maybe there are locks on the file system that prevents node to write properly?)
You could try to make everything sequential and only write weekJson once instead of everytime you go over an item:
EDIT
I updated my original code proposition by keeping parallel calls and it worked for me (it's similar to OP's code but I only write the json file once per week).
Then I tried to run OP's code and it was working fine as well. So this makes me think that the problem isn't from the code itself but rather how it's called. As a pure node script, there doesn't seem to be any issue. But I just noticed that OP is using it server side as the result of an API call.
Having an API write so many JSON concurrently is probably not the best idea (especially if the api is called multiple times almost simultaneously). You could either
just return the games in the response
or precompute the results
or fetch and write them only once then cache the result to be reused
Then I wonder if due to the server context, there is not some kind of timeout since OP said that with my initial solution, only the first week was created.
const axios = require("axios");
const fs = require("fs");
async function writeGames() {
const writeWeekGamesPromises = [];
// iterate 18 times
for (let weekNumber = 1; weekNumber < 19; weekNumber++) {
// give week a default value in case the json file doesn't exist (for repro purpose)
let week = "{}";
try {
week = fs.readFileSync(`./pickem/week${weekNumber}.json`, "utf8");
} catch (e) {
console.log(`error reading week ${weekNumber} json file:`, e);
// file doesn't exist yet
}
const weekJson = JSON.parse(week);
// empty weekJson.games array
const games = [];
weekJson.games = games;
// get all items
// Add await keyword to wait for a week to be processed before going to the next one
writeWeekGamesPromises.push(axios
.get(
`https://sports.core.api.espn.com/v2/sports/football/leagues/nfl/seasons/2022/types/2/weeks/${weekNumber}/events?lang=en&region=us`
)
.then(async (eventListResponse) => {
// add async to be able to use await
const schedule = [];
console.log(JSON.stringify(eventListResponse.data),'\n');
// get all items from response
const items = eventListResponse.data.items;
// console.log(eventListResponse.data.items); // this seems to be useless since we log the whole data just above
// parallelize calls and wait for all games from a week to be fetched before writing the file
await Promise.all(
items.map((item) => {
// we return the promise so that Promise.all will wait for all games to be pushed before going on writing the file
return axios
.get(item.$ref)
.then((response) => {
// get name, date and eventid
const {name, date, id: eventid} = response.data;
// get team ids
let team1 = response.data.competitions[0].competitors[0].id;
let team2 = response.data.competitions[0].competitors[1].id;
games.push({ name, date, eventid, team1, team2 });
})
.catch((error) => {
console.log(error);
});
})
);
// Now that all game data is ready, write in the file
fs.writeFileSync(
`./pickem/week${weekNumber}.json`,
JSON.stringify(weekJson)
);
})
.catch((error) => {
console.log(error);
}));
}
// Waiting for all games from all weeks to be processed
await Promise.all(writeWeekGamesPromises);
}
async function runAndLogTime() {
const start = Date.now();
await writeGames();
console.log(`took ${(Date.now() - start) / 1000}s to write all json files`);
}
runAndLogTime();

Getting undefined when adding input text values into array

In a React project, I'm displaying certain records in a table which also has input text boxes for changing the values when needed. To process those changed records it needs to be added into an array, but, getting undefined when changed the values. Although each record is associated with unique id, unable to add in new array. Please refer to the code below.
const textChange = (data) => {
const { id, value } = data;
setDataNew((prevInfo) => {
// Here the records are getting undefined and not getting added into array
const dataIndex = id - 1;
prevInfo[dataIndex] = value;
return [...prevInfo];
});
};
Any suggestions and solution highly appreciated.
Please refer to code sandbox link for better clarity --> https://codesandbox.io/s/elated-varahamihira-xpjtdb?file=/src/Table.js:757-959

If I understood it correctly here is what you need to do if you need all the records which got updated :
const textChange = (data) => {
const { id, value } = data;
setDataNew((prevInfo) => {
const newList = [...prevInfo];
const index = newList.findIndex((datum) => datum.id === id);
if (index !== -1) {
newList[index] = { id, value };
} else {
newList.push({ id, value });
}
return [...newList];
});
};
Mistake in your code
You were getting undefined because you were calculating index like :
const dataIndex = id - 1;
if the changed object id was 6708 , you were adding element at 6707th index. Hence all first 6706 element were showing up as undefined.
Link : working demo

Why's my variable giving an undefined error when it's really not undefined?

I cannot figure out for the life of me how PackId is undefined according to the error: TypeError: Cannot read property 'PackId' of undefined.
What I'm doing here is: I'm deleting an object that's inside of a collection (which's happening successfully) but I'd also like to eventually display the response correctly which should consist of packIdsOwned and packsOwnedMetadata arrays being populated.
Why's PackId null in the packIdsOwned.push(packsOwned[i].PackId); line and how can I fix it?
const db = client.db("myDb");
let collection = db.collection("Players");
let result = null;
let packIdsOwned = [];
let packsOwnedMetadata = [];
let packIdInput = Profile.PackIdInput; // user input
let packsOwned = result.packsOwned;
// Delete object in the document
collection.updateOne({"userName": result['userName']}, { $pull: { packsOwned: { PackId: packIdInput }}});
// Remove the pack ID from the response that's been deleted in the document
for(let i = 0; i < packsOwned.length; i++) {
if (packsOwned[i].PackId == packIdInput) {
let removePackId = packsOwned.splice(i, 1); // find the PackId in the document and delete it
removePackId = null;
}
// this is for the response but the below line is throwing off the whole program
packIdsOwned.push(packsOwned[i].PackId); // it's saying this PackId value is null
packsOwnedMetadata.push({
PackID : packsOwned[i].PackId
});
}

You remove the index and than you are trying to read that element you just removed.
let removePackId = packsOwned.splice(i, 1); <-- You remove it
packIdsOwned.push(packsOwned[i].PackId); <-- You try to read it.

Adding more elements to an object in javascript

Context: I'm fetching 'car' data below (see the code that starts with "for") from a GET request and am pushing it to the 'array' array. And for each car.ID that I get, I need to run another GET request in sequence (the GET uses car.ID as a parameter and I have no problems in doing this).
Problem: after I fetch the results from the second GET, how to push the data to the same object of the array (i.e. I want to "complement" the object above that ended on car.BrandID by adding a few more key: value pairs to the same "line")?
THANK YOU IN ADVANCE.
for (let car of carsJustObtained) {
for (i=0; i<=2; i++){
array.push(
{
timestamp: epoch,
ID : car.ID,
BrandID : car.BrandID
})
//code continues but don't worry
FULL CODE BELOW:
function gotCars(carsJustObtained) {
for (let car of carsJustObtained) {
for (i=0; i<=2; i++){
array.push(
{
timestamp: epoch,
ID : car.ID,
BrandID : car.BrandID,
ModelID : car.ModelID,
}
);
//given car.ID the second GET will be triggered because the path depends on this variable!
let path_get_all_prices = `xxx=${car.ID}?securityToken=xxx&vehiclePriceTypeID=xxx`;
let get = https.get(
{
hostname: 'xxx.com',
path: path_get_all_prices
},
(getRes) => {
console.log(`getting prices for car ${car.ID}...`);
var reply = "";
getRes.on("data", (chunk) => (reply += chunk));
const obj = JSON.parse(reply);
gotPrices(obj.Response);
}
);
function gotPrices(pricesJustObtained) {
for (let price of pricesJustObtained){
array.push(
//how to add results to the same array of the 1st GET? There are three 'prices' for each car.ID
)};
};
};

You have to find the index of your object in your array, then you can add everything you can to this object :
array[index].name = 'Hello';

There are many ways to do this. I recommend you read about array.map()
This function lets you iterate your array and in each iteration perform the get request and extend the current element.

The key is to recognise that you are not pushing, the second time
What you are doing is reading each element of the array, and adding some information to that element.
for (let car of carsJustObtained) {
const newInfo=getFurtherInformationAboutCar(car) // this is your second getting
car.newInfo1 = newInfo.param1;
car.newInfo2 = newInfo.param2;
car.newInfo3 = newInfo.param3;
}
To answer your specific question about "merging" information
If you have one set of properties already defined for the car, and you want to merge in multiple new properties, a simple way to do it is as follows:
car = { ...car, ...objectContainingNewProperties};
If your original car was {a:2, b:3, c:4} and objectContainingNewProperties was {c: 10, d:20, e:30}, the result would be:
{ a:2,
b:3,
c:10,
d:20,
e:30 }
Any same-named properties in the second object will overwrite those in the original object.

Your second request is of course asynchronous, so by the time you get its response, you have already populated your array with all information from the first request.
I would suggest to use a promise-enabled alternative to http.get, as promises are a native feature in JavaScript that makes working with asynchronous events less messy. I will show here how it can work with node-fetch.
As fetch is natively supported in browser agents, you can run the snippet below to see the result. As a demo I have used https://jsonplaceholder.typicode.com/ as a server resource: it returns JSON for several sample datasets, including todos and users. A todo has some properties (like a title) and has a user id. A user has an email and a username. So we could make the todos-request the first request, and the users-request the second one (based on the user id received in the first). So the principle is the same as with your cars and prices.
This relies heavily on promises:
// For demo, we use these two URls:
// They both need a number following it
let url1 = "https://jsonplaceholder.typicode.com/todos/";
let url2 = "https://jsonplaceholder.typicode.com/users/";
let promises = [];
// Let's say we build an array with 5 objects:
for (let i = 1; i <= 5; i++) {
promises.push(
// Make the request
fetch(url1 + i*30)
// Parse the response as JSON
.then(resp => resp.json())
// Process this data
.then(data => {
// Create our own object from this data
let obj = {
user: data.userId,
todo: data.title
};
// Make second request, to get user's email, joining it with obj
return Promise.all([obj, fetch(url2 + obj.user)])
})
.then(([obj, resp2]) => Promise.all([obj, resp2.json()]))
// Merge the new data with the old
.then(([obj, data2]) => Object.assign(obj, {
email: data2.email,
logon: data2.username
}))
);
}
// Wait for all requests to finish...
Promise.all(promises).then(results => {
console.log(results); // The result!
});
With async/await
The above can be made even more readable, if you use the async/await syntax:
let url1 = "https://jsonplaceholder.typicode.com/todos/";
let url2 = "https://jsonplaceholder.typicode.com/users/";
async function getOne(i) {
let resp = await fetch(url1 + i*30);
let data = await resp.json();
// Create object from first request
let obj = {
user: data.userId,
todo: data.title
};
// Make second request, joining it with obj
let resp2 = await fetch(url2 + obj.user);
let data2 = await resp2.json();
return Object.assign(obj, {
email: data2.email,
logon: data2.username
});
}
let promises = [];
for (let i = 1; i <= 5; i++) {
promises.push(getOne(i));
}
Promise.all(promises).then(results => {
console.log(results);
});

Continue on Null Value of Result (Nodejs, Puppeteer)

I'm just starting to play around with Puppeteer (Headless Chrome) and Nodejs. I'm scraping some test sites, and things work great when all the values are present, but if the value is missing I get an error like:
Cannot read property 'src' of null (so in the code below, the first two passes might have all values, but the third pass, there is no picture, so it just errors out).
Before I was using if(!picture) continue; but I think it's not working now because of the for loop.
Any help would be greatly appreciated, thanks!
for (let i = 1; i <= 3; i++) {
//...Getting to correct page and scraping it three times
const result = await page.evaluate(() => {
let title = document.querySelector('h1').innerText;
let article = document.querySelector('.c-entry-content').innerText;
let picture = document.querySelector('.c-picture img').src;
if (!document.querySelector('.c-picture img').src) {
let picture = 'No Link'; } //throws error
let source = "The Verge";
let categories = "Tech";
if (!picture)
continue; //throws error
return {
title,
article,
picture,
source,
categories
}
});
}

let picture = document.querySelector('.c-picture img').src;
if (!document.querySelector('.c-picture img').src) {
let picture = 'No Link'; } //throws error
If there is no picture, then document.querySelector() returns null, which does not have a src property. You need to check that your query found an element before trying to read the src property.
Moving the null-check to the top of the function has the added benefit of saving unnecessary calculations when you are just going to bail out anyway.
async function scrape3() {
// ...
for (let i = 1; i <= 3; i++) {
//...Getting to correct page and scraping it three times
const result = await page.evaluate(() => {
const pictureElement = document.querySelector('.c-picture img');
if (!pictureElement) return null;
const picture = pictureElement.src;
const title = document.querySelector('h1').innerText;
const article = document.querySelector('.c-entry-content').innerText;
const source = "The Verge";
const categories = "Tech";
return {
title,
article,
picture,
source,
categories
}
});
if (!result) continue;
// ... do stuff with result
}
Answering comment question: "Is there a way just to skip anything blank, and return the rest?"
Yes. You just need to check the existence of each element that could be missing before trying to read a property off of it. In this case we can omit the early return since you're always interested in all the results.
async function scrape3() {
// ...
for (let i = 1; i <= 3; i++) {
const result = await page.evaluate(() => {
const img = document.querySelector('.c-picture img');
const h1 = document.querySelector('h1');
const content = document.querySelector('.c-entry-content');
const picture = img ? img.src : '';
const title = h1 ? h1.innerText : '';
const article = content ? content.innerText : '';
const source = "The Verge";
const categories = "Tech";
return {
title,
article,
picture,
source,
categories
}
});
// ...
}
}
Further thoughts
Since I'm still on this question, let me take this one step further, and refactor it a bit with some higher level techniques you might be interested in. Not sure if this is exactly what you are after, but it should give you some ideas about writing more maintainable code.
// Generic reusable helper to return an object property
// if object exists and has property, else a default value
//
// This is a curried function accepting one argument at a
// time and capturing each parameter in a closure.
//
const maybeGetProp = default => key => object =>
(object && object.hasOwnProperty(key)) ? object.key : default
// Pass in empty string as the default value
//
const getPropOrEmptyString = maybeGetProp('')
// Apply the second parameter, the property name, making 2
// slightly different functions which have a default value
// and a property name pre-loaded. Both functions only need
// an object passed in to return either the property if it
// exists or an empty string.
//
const maybeText = getPropOrEmptyString('innerText')
const maybeSrc = getPropOrEmptyString('src')
async function scrape3() {
// ...
// The _ parameter name is acknowledging that we expect a
// an argument passed in but saying we plan to ignore it.
//
const evaluate = _ => page.evaluate(() => {
// Attempt to retrieve the desired elements
//
const img = document.querySelector('.c-picture img');
const h1 = document.querySelector('h1')
const content = document.querySelector('.c-entry-content')
// Return the results, with empty string in
// place of any missing properties.
//
return {
title: maybeText(h1),
article: maybeText(article),
picture: maybeSrc(img),
source: 'The Verge',
categories: 'Tech'
}
}))
// Start with an empty array of length 3
//
const evaluations = Array(3).fill()
// Then map over that array ignoring the undefined
// input and return a promise for a page evaluation
//
.map(evaluate)
// All 3 scrapes are occuring concurrently. We'll
// wait for all of them to finish.
//
const results = await Promise.all(evaluations)
// Now we have an array of results, so we can
// continue using array methods to iterate over them
// or otherwise manipulate or transform them
//
results
.filter(result => result.title && result.picture)
.forEach(result => {
//
// Do something with each result
//
})
}

Try-catch worked for me:
try {
if (await page.$eval('element')!==null) {
const name = await page.$eval('element')
}
}catch(error){
name = ''
}