Benchmark: map index vs spread copy index

HTML Preparation code:

<script src=''></script>

Tests:

map
const a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; const b = a.map((x, i) => i !== 3 ? x : 99);
spread
const a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; const c = [...a]; c[3] = 99;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
map
spread

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_3) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.0.5 Safari/605.1.15

Browser/OS: Safari 13 on Mac OS X 10.15.3

View result in a separate tab

Test name	Executions per second
map	5859015.0 Ops/sec
spread	19477002.0 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one month ago):

LLMs can make mistakes. Check important info.

**Overview of the Benchmark**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided benchmark measures the performance difference between two approaches: using the `map()` method with an index check, and using the spread operator (`...`) followed by modifying the array.

**What is tested?**

The benchmark tests how fast each approach creates a new copy of the original array, modifies it, and returns the result. The test cases are:

1. **`map()` with index check**: This approach uses the `map()` method to create a new array with elements from the original array, but only for certain indices (i.e., excluding index 3). The function passed to `map()` checks if the current index is not equal to 3, and returns either the original element or a default value (99) depending on the condition.
2. **Spread operator (`...`) with array modification**: This approach uses the spread operator to create a new copy of the original array, modifies it by changing the third element to 99, and then returns the modified array.

**Options compared**

The benchmark compares two approaches:

1. **`map()` method with index check**
	* Pros:
		+ Easy to understand and implement
		+ Can be useful in scenarios where you need to modify elements of an array based on conditions
	* Cons:
		+ May involve more overhead due to the callback function and index checking
		+ Returns a new array with modified elements, which might not be what you expect if you're expecting a new array without changes
2. **Spread operator (`...`) followed by array modification**
	* Pros:
		+ Creates a shallow copy of the original array, which can be faster and more memory-efficient than `map()`
		+ Allows for direct modification of elements in the resulting array
	* Cons:
		+ Requires creating an intermediate array using the spread operator
		+ Might involve more overhead due to the creation of a new array

**Library usage**

The benchmark uses none.

**Special JavaScript features or syntax**

None are explicitly mentioned, but the use of the spread operator (`...`) is a modern JavaScript feature that can be considered special. The `map()` method with index checking also relies on ES6+ syntax.

**Alternative approaches**

Other alternatives to consider when working with arrays and modifying elements include:

1. **Using `Array.prototype.forEach()`**: This approach is similar to using `map()` but doesn't return a new array.
2. **Using `Array.prototype.filter()`**: This approach can be used to create a new array with only the desired elements, without changing the original array.
3. **Using `reduce()`**: This approach can be used to transform an array into a new value, such as summing or concatenating elements.

Keep in mind that these alternatives may have different performance characteristics and use cases compared to the approaches tested in the benchmark.

Related benchmarks:

map index vs spread copy index (version: 0)

Comparing performance of: map vs spread

Created: 4 years ago by: Guest

Jump to the latest result

map

spread

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one month ago):