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Why javascript array sort doesn't compare all elements with each other?

I'm trying to understand why Javascript array sort doesn't work with the following logic. I have no problems making my own algorithm to sort this array, but I'm trying to make it with the Javascript sort built-in method to understand it better.
In this code, I want to push entities that "belongs to" another entity to the bottom, so entities that "has" other entities appear on the top. But apparently, the sort method doesn't compare all elements with each other, so the logic doesn't work properly.
Am I doing something wrong, or it is the correct behavior for the Javascript sort method?
The code I'm trying to execute:
let entities = [
{
name: 'Permission2',
belongsTo: ['Role']
},
{
name: 'Another',
belongsTo: ['User']
},
{
name: 'User',
belongsTo: ['Role', 'Permission2']
},
{
name: 'Teste',
belongsTo: ['User']
},
{
name: 'Role',
belongsTo: ['Other']
},
{
name: 'Other',
belongsTo: []
},
{
name: 'Permission',
belongsTo: ['Role']
},
{
name: 'Test',
belongsTo: []
},
]
// Order needs to be Permission,
let sorted = entities.sort((first, second) => {
let firstBelongsToSecond = first.belongsTo.includes(second.name),
secondBelongsToFirst = second.belongsTo.includes(first.name)
if(firstBelongsToSecond) return 1
if(secondBelongsToFirst) return -1
return 0
})
console.log(sorted.map(item => item.name))
As you can see, "Role" needs to appear before "User", "Other" before "Role", etc, but it doesn't work.
Thanks for your help! Cheers

You're running into literally how sorting is supposed to work: sort compares two elements at a time, so let's just take some (virtual) pen and paper and write out what your code is supposed to do.
If we use the simplest array with just User and Role, things work fine, so let's reduce your entities to a three element array that doesn't do what you thought it was supposed to do:
let entities = [
{
name: 'User',
belongsTo: ['Role', 'Permission2']
},
{
name: 'Test',
belongsTo: []
},
{
name: 'Role',
belongsTo: ['Other']
}
]
This will yield {User, Test, Role} when sorted, because it should... so let's see why it should:
pick elements [0] and [1] from [user, test, role] for comparison
compare(user, test)
user does not belong to test
test does not belong to user
per your code: return 0, i.e. don't change the ordering
we slide the compare window over to [1] and [2]
compare(test, role)
test does not belong to role
role does not belong to test
per your code: return 0, i.e. don't change the ordering
we slide the compare window over to [2] and [3]
there is no [3], we're done
The sorted result is {user, test, role}, because nothing got reordered
So the "bug" is thinking that sort compares everything-to-everything: as User and Role are not adjacent elements, they will never get compared to each other. Only adjacent elements get compared.

update multiple different documents in mongodb (nodejs backend) [duplicate]

This question already has answers here:
MongoDB: How to update multiple documents with a single command?
(13 answers)
Closed 3 years ago.
I looked at other questions and I feel mine was different enough to ask.
I am sending a (potentially) large amount of information back to my backend, here is an example data set:
[ { orders: [Array],
_id: '5c919285bde87b1fc32b7553',
name: 'Test',
date: '2019-03-19',
customerName: 'Amego',
customerPhone: '9991112222',
customerStreet: 'Lost Ave',
customerCity: 'WestZone',
driver: 'CoolCat',
driverReq: false, // this is always false when it is ready to print
isPrinted: false, // < this is important
deliveryCost: '3',
total: '38.48',
taxTotal: '5.00',
finalTotal: '43.48',
__v: 0 },
{ orders: [Array],
_id: '5c919233bde87b1fc32b7552',
name: 'Test',
date: '2019-03-19',
customerName: 'Foo',
customerPhone: '9991112222',
customerStreet: 'Found Ave',
customerCity: 'EastZone',
driver: 'ChillDog',
driverReq: false,// this is always false when it is ready to print
isPrinted: false, // < this is important
deliveryCost: '3',
total: '9.99',
taxTotal: '1.30',
finalTotal: '11.29',
__v: 0 },
{ orders: [Array],
_id: '5c91903b6e0b7f1f4afc5c43',
name: 'Test',
date: '2019-03-19',
customerName: 'Boobert',
customerPhone: '9991112222',
customerStreet: 'Narnia',
customerCity: 'SouthSzone',
driver: 'SadSeal',
driverReq: false,// this is always false when it is ready to print
isPrinted: false, // < this is important
deliveryCost: '3',
total: '41.78',
taxTotal: '5.43',
finalTotal: '47.21',
__v: 0 } ] }
My front end can find all the orders that include isPrinted:false, I then allow the end user to 'print' all the orders that are prepared, in which, I need to change isPrinted into true, that way when I pull up a next batch I won't have reprints.
I was looking at db.test.updateMany({foo: "bar"}, {$set: {isPrinted: true}}), and I currently allow each order to set a new driver, which I update by:
Order.update({
_id: mongoose.Types.ObjectId(req.body.id)
},
{
$set: {
driver:req.body.driver, driverReq:false
}
which is pretty straight forward, as only 1 order comes back at a time.
I have considered my front end doing a foreach and posting each order individually, then updating the isPrinted individually but that seems quite inefficient. Is there a elegant solutions within mongo for this?
I'm not sure how I would user updateMany considering each _id is unique, unless I grab all the order's who are both driverReq:false and isPrinted:false (because that is the case where they are ready to print.

I found a solution, that was in fact using UpdateMany.
Order.updateMany({
isPrinted: false, driverReq:false
},
{
$set: {
isPrinted: true
}
consider there this special case where both are false when it needs to be changed too true. But I do wonder if there is a way to iterate over multiple document id's with ease.

Convert Papaparse rows to objects

Does papaparse support return an array of object instances that are keyed by the header columns?
For example I have a CSV file like this:
sku, location, quantity
'sku1', 'Chicago', 3
'sku2', 'New York, 4
I'd like the array returned by papaparse to look like this:
[{sku: 'sku1', location: 'Chicago', quantity: 3}, ...]
This should also be possible:
results[0].sku == 'sku1'
results[1].quantity == 4

Try adding header: true to the config parameter.
From the docs:
header: If true, the first row of parsed data will be interpreted as field names. An array of field names will be returned in meta, and each row of data will be an object of values keyed by field name instead of a simple array. Rows with a different number of fields from the header row will produce an error. Warning: Duplicate field names will overwrite values in previous fields having the same name.
For example:
Papa.parse('./data.csv', {
download: true,
header: true, // gives us an array of objects
dynamicTyping: true,
complete: ({ data }) => console.log(data),
});
given your data should yield
[
{
sku: 'sku1',
location: 'Chicago',
quantity: 3,
},
{
sku: 'sku2',
location: 'New York',
quantity: 4,
},
]

It is possible by few line in simple javascript working example:
My csv file data:
sku, location, quantity
'sku1', 'Chicago', 3
'sku2', 'New Yoark, 4

Prevent Javascript function running out of memory because too many objects

I'm building a web scraper in nodeJS that uses request and cheerio to parse the DOM. While I am using node, I believe this is more of a general javascript question.
tl;dr - creating ~60,000 - 100,000 objects, uses up all my computer's RAM, get an out of memory error in node.
Here's how the scraper works. It's loops within loops, I've never designed anything this complex before so there might be way better ways to do this.
Loop 1: Creates 10 objects in array called 'sitesArr'. Each object represents one website to scrape.
var sitesArr = [
{
name: 'store name',
baseURL: 'www.basedomain.com',
categoryFunct: '(function(){ // do stuff })();',
gender: 'mens',
currency: 'USD',
title_selector: 'h1',
description_selector: 'p.description'
},
// ... x10
]
Loop 2: Loops through 'sitesArr'. For each site it goes to the homepage via 'request' and gets a list of category links, usually 30-70 URLs. Appends these URLs to the current 'sitesArr' object to which they belong, in an array property whose name is 'categories'.
var sitesArr = [
{
name: 'store name',
baseURL: 'www.basedomain.com',
categoryFunct: '(function(){ // do stuff })();',
gender: 'mens',
currency: 'USD',
title_selector: 'h1',
description_selector: 'p.description',
categories: [
{
name: 'shoes',
url: 'www.basedomain.com/shoes'
},{
name: 'socks',
url: 'www.basedomain.com/socks'
} // x 50
]
},
// ... x10
]
Loop 3: Loops through each 'category'. For each URL it gets a list of products links and puts them in an array. Usually ~300-1000 products per category
var sitesArr = [
{
name: 'store name',
baseURL: 'www.basedomain.com',
categoryFunct: '(function(){ // do stuff })();',
gender: 'mens',
currency: 'USD',
title_selector: 'h1',
description_selector: 'p.description',
categories: [
{
name: 'shoes',
url: 'www.basedomain.com/shoes',
products: [
'www.basedomain.com/shoes/product1.html',
'www.basedomain.com/shoes/product2.html',
'www.basedomain.com/shoes/product3.html',
// x 300
]
},// x 50
]
},
// ... x10
]
Loop 4: Loops through each of the 'products' array, goes to each URL and creates an object for each.
var product = {
infoLink: "www.basedomain.com/shoes/product1.html",
description: "This is a description for the object",
title: "Product 1",
Category: "Shoes",
imgs: ['http://foo.com/img.jpg','http://foo.com/img2.jpg','http://foo.com/img3.jpg'],
price: 60,
currency: 'USD'
}
Then, for each product object I'm shipping them off to a MongoDB function which does an upsert into my database
THE ISSUE
This all worked just fine, until the process got large. I'm creating about 60,000 product objects every time this script runs, and after a little while all of my computer's RAM is being used up. What's more, after getting about halfway through my process I get the following error in Node:
FATAL ERROR: CALL_AND_RETRY_2 Allocation failed - process out of memory
I'm very much of the mind that this is a code design issue. Should I be "deleting" the objects once I'm done with them? What's the best way to tackle this?

How to parse below JSON

How to parse below JSON code in JavaScript where iterators are not identical?
var js= {
'7413_7765': {
availableColorIds: [ '100', '200' ],
listPrice: '$69.00',
marketingMessage: '',
prdId: '7413_7765',
prdName: 'DV by Dolce Vita Archer Sandal',
rating: 0,
salePrice: '$59.99',
styleId: '7765'
},
'0417_2898': {
availableColorIds: [ '249', '203' ],
listPrice: '$24.95',
marketingMessage: '',
prdId: '0417_2898',
prdName: 'AEO Embossed Flip-Flop',
rating: 4.5,
salePrice: '$19.99',
styleId: '2898'
},
prod6169041: {
availableColorIds: [ '001', '013', '800' ],
listPrice: '$89.95',
marketingMessage: '',
prdId: 'prod6169041',
prdName: 'Birkenstock Gizeh Sandal',
rating: 5,
salePrice: '$79.99',
styleId: '7730'
}
}
How can I parse this JSON in JavaScript? I want the values of prdName, listprice, salePrice in JavaScript?

var products = js; // more semantic
for (productId in products){
var product = products[productId];
console.log (product.prdName , product.listprice, product.salePrice);
}
js is an Object, the for (key in instance) iteration moves through the first level object's attributes, in this case 7413_7765, 0417_2898 and prod6169041, this keys are stored in the var productId, so products[productId] will return the value of this attributes.
Note that the "" in object keynames are not necesary.

You have already assigned the JSON to an object js.
You're trying to loop through JavaScript object, as Edorka mentioned iterate it.