All Questions
62
questions
4
votes
2
answers
120
views
Why is pre-allocation of arrays slower than dynamic pushing in JavaScript?
I have been testing two methods of array creation and initialization in JavaScript using Node.js. One method involves dynamically pushing elements into the array, while the other method involves pre-...
- 438
1
vote
1
answer
219
views
In V8 JS, do packed arrays of objects (PACKED_ELEMENTS) reserve consecutive system memory if all elements are the same hidden class?
For example:
const array = [];
for(let i = 0; i<20000; i++)
array.push({x:1.2, y:3.4, t:123+i});
The hidden class of each element would be: [double, double, small integer].
Are the contents ...
- 119
1
vote
1
answer
117
views
JavaScript Objects and Sorted Integer Keys under the hood
I have searched a bunch of other resources but have not been able to find a quality answer to this question.
JavaScript objects sort their integer keys in ascending order, not insertion order.
const ...
- 113
1
vote
2
answers
289
views
V8 engine: why object spread at the start of new object create new hidden classes only after ninth element? Otherwise if spread at the end - its ok
I just read about hidden classes and inline caching. I found interesting performance thing, that break my mind.
So, we have the following code:
const n = 100000;
const array = [];
for (let i = 0; i &...
17
votes
1
answer
1k
views
JavaScript array performance drop at 13k-16k elements
I am doing some performance testing regarding creating and editing performance of arrays and noticed that there are some weird characteristics around arrays with about 13k-16k elements.
The below ...
- 1,559
0
votes
0
answers
421
views
Use spread operator over a spread operator on an 2-d array [duplicate]
Is there a way to use a spread operator over another spread operator?
const arr = [[1,2,3],[4],[5,6],[7,8,9]];
const spreadArr = [...arr]; // This works
console.log(spreadArr); // [[1,2,3],[4],[5,6],[...
- 2,885
0
votes
1
answer
124
views
How to introspect elements kind in an array in V8
After reading this article: https://v8.dev/blog/elements-kinds. I was wondering if some of the arrays that are created in my code are packed or holey. Is there any way to check this at runtime in a ...
- 243
10
votes
1
answer
12k
views
Time complexity of Javascript Array.find() in modern browsers
Since array.find() iterates over an array, if I handle (potentially) large arrays, I always make sure to have an indexed object like so:
{ [id:string]: Item }
if I need to look up items by id in ...
- 2,634
0
votes
0
answers
45
views
Any way to force js engines to unroll a loop? [duplicate]
I have a performance critical queue container that does a lot of random inserts/deletes. In my container class, I have a fixed size Uint32Array called updates and in my insert logic, I need to compare ...
- 6,485
3
votes
1
answer
336
views
Is an array of ints actually implemented as an array of ints in JavaScript / V8?
There is claim in this article that an array of ints in JavaScript is implemented by a C++ array of ints.
However; According to MDN unless you specifically use BigInts, in JavaScript all numbers are ...
- 51
1
vote
3
answers
223
views
Extract subarray of Columns from a multidimensional array and mutate the original array to remove those columns JavaScript
I want to extract a subarray of Columns from a multidimensional array and mutate the original array to remove those columns in JavaScript
Ex: If I have an array
originalArray =
[
[A, B, C, D, E, F],
...
- 758
0
votes
1
answer
388
views
Nodejs c++ addon: Not able to access Array elements
I want to access the elements of an array that is passed in a function as an arg from the js side.
The code is like this:
void Method(const FunctionCallbackInfo<Value> &args){
Isolate* ...
- 455
1
vote
0
answers
18
views
Storing shuffled arrays in a parrent array [duplicate]
Problem : Main array have identical arrays instead of shuffle arrays after shuffling
// Initiating an empty array
const mainArr = []
// Random array with any values
const arr = [1, 2, 3, 4, 5]
/...
- 11
5
votes
1
answer
3k
views
Object.entries() time complexity
Does anyone know the complexity of Object.entries() in Javascript? Based on this question I'd guess at maybe O(n) as well if it's implemented by obtaining the keys and values as arrays then zipping ...
- 2,849
2
votes
2
answers
725
views
Why is if(1) faster than if(true)
I'm trying to make Conway's game of life in JavaScript and canvas, I have a matrix of 1280x720 that I use to store cells data, I'm currently storing the data as 1 = alive, 0 = dead, and then when I ...
- 331