Optimizing memory consumption in JavaScript

All created variables are stored in the computer RAM. Sometimes thoughtlessly writing code can dramatically increase memory consumption.

Let's look at an example. Let us face the task of finding the sum of integers from 1 to 100000000. Let's say we have a function that fills an array with integers from a given range:

function fillArr(a, b) {
	let res = [];
	
	for (let i = a; i <= b; i++) {
		res.push(i);
	}
	
	return res;
}

Let's also have a function that finds the sum of the array elements:

function getSum(arr) {
	let sum = 0;
	
	for (let elem of arr) {
		sum += elem
	}
	
	return sum;
}

With a combination of these functions, you can easily solve the problem:

let sum = getSum(fillArr(1, 100000000));

It turned out to be an elegant solution. However, it has a problem: it consumes a huge amount of RAM.

Let's count. The fillArr function creates an array with 100000000 numbers. Let JavaScript allocate 2 bytes per number - then our array will need 200000000 bytes to store, which is something like 200 megabytes of RAM.

But in fact, much more RAM will be needed due to the fact that JavaScript has a very large overhead when storing an array.

Understanding the problem, it is easy to make a function that solves the problem and practically doesn't consume RAM:

function getNumsSum(max) {
	let sum = 0;
	
	for (let i = 1; i <= max; i++) {
		sum += i;
	}
	
	return sum;
}

Let's solve the problem using our function:

let sum = getNumsSum(100000000);

A certain programmer was faced with the task of finding the number of numbers divisible by 7 without a remainder that are in a given range. He solved it like this:

let arr = [];

for (let i = 0; i <= 1000; i++) {
	if (i % 7 == 0) {
		arr.push(i);
	}
}

console.log(arr.length);

Explain what is wrong with this code. Modify the code to a better one.

A certain programmer was faced with the task of finding the sum of the divisors of a number. He solved it like this:

function getDivisors(num) {
	let res = [];
	
	for (let i = 1; i <= num; i++) {
		if (num % i === 0) {
			res.push(i);
		}
	}
	
	return res;
}

function getSum(arr) {
	let sum = 0;
	
	for (let elem of arr) {
		sum += elem
	}
	
	return sum;
}

let sum = getSum(getDivisors(320));
console.log(sum);

Explain what is wrong with this code. Modify the code to a better one.