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`Array.slice(0, N)` vs `Array.length = N` sd4343
(version: 0)
Comparing performance of:
`Array.slice(0, N)` vs `Array.length = N`
Created:
3 years ago
by:
Guest
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Script Preparation code:
var arr = ["1","2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17","18","19","20","21","22"];
Tests:
`Array.slice(0, N)`
arr.slice(0, 20);
`Array.length = N`
arr.length = 20;
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
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Test case name
Result
`Array.slice(0, N)`
`Array.length = N`
Fastest:
N/A
Slowest:
N/A
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's break down the provided benchmark and explain what's being tested. **Overview** The benchmark compares two approaches for creating an array with a fixed length in JavaScript: 1. `arr.slice(0, N)` (without assigning to a variable) 2. `arr.length = N` (assigning a value to the `length` property) **Options Compared** Both approaches create an array with 20 elements initialized with numbers from 1 to 20. * Option 1: `arr.slice(0, 20)` creates a new array and copies the first 20 elements of the original array (`var arr = [...]`) into it. The `slice` method returns a shallow copy of the specified portion of an array. * Option 2: `arr.length = N` assigns a value to the `length` property, but does not create any actual array elements. This approach only sets the length of the array without populating it. **Pros and Cons** * **Option 1 (Array slicing)**: + Pros: creates an actual array with elements, which can be used in further operations. + Cons: may incur additional memory allocation and copying overhead due to creating a new array. * **Option 2 (Assigning `length` property)**: + Pros: faster and more lightweight, as it only sets the length without creating any elements. + Cons: does not create an actual array with elements, which may limit its usefulness. **Library** None of the provided benchmark uses a library. However, if you're using modern JavaScript features like `Array.from()` or `Array.prototype.fill()`, they might be used in other benchmarks. **Special JS Feature/Syntax (Not Applicable)** Since neither test case uses any special JavaScript features or syntax, there's nothing to explain here. **Other Alternatives** Alternative approaches for creating arrays with a fixed length include: * Using the spread operator (`[...Array(N)]`): creates an array filled with `N` elements. * Using `Array(N)`: creates an array filled with `N` elements (this is similar to Option 2, but the `length` property is not set directly). * Using a loop: creates an array by iterating over a range of numbers and assigning each one to an element. Keep in mind that these alternatives might have different performance characteristics depending on the specific use case.
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