Benchmark: Array.from vs construct manually

Script Preparation code:

var src = Object.keys([...Array(10000)]);
var z = {};

Tests:

Array.from
z.z = Array.from(src[Symbol.iterator]());
manual
let n = src.length; let a = Array(n); let iter = src[Symbol.iterator](); for (let i = 0; i < n; ++i) {a[i] = iter.next().value;}; z.z = a;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array.from
manual

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's break down the benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark is comparing two approaches to create an array from scratch:

1. `Array.from`: This method takes an iterable object (like an array or a string) and creates a new array with all its elements.
2. Manual approach: Instead of using `Array.from`, the code creates an empty array (`z.z = {}`) and then iterates over the input data to populate it.

**Options being compared**

The two options being compared are:

* `Array.from`: A built-in method that creates a new array from an iterable object.
* Manual approach: Creating an array manually by iterating over the input data.

**Pros and Cons of each approach**

**`Array.from`**

Pros:

* Concise and readable code
* Less error-prone, as it handles edge cases for you

Cons:

* May incur overhead due to method invocation and object lookup
* Might be slower than a custom implementation due to the overhead of the `for...of` loop (more on this later)

**Manual approach**

Pros:

* Can be optimized for performance, especially when working with large datasets
* Allows direct control over memory allocation and iteration

Cons:

* More verbose and error-prone code
* Requires manual management of array indices and edge cases

**Other considerations**

In modern JavaScript, using `Array.from` is generally a good choice, as it's concise and readable. However, when working with very large datasets or performance-critical code, a custom implementation might be necessary to squeeze out every last bit of optimization.

**Library usage**

There is no library being used in this benchmark.

**Special JavaScript features/syntax**

The `Symbol.iterator` syntax is used to access the iterator protocol for the input data (`src`). This allows us to iterate over the array-like object without explicitly creating an array.

However, it's worth noting that the `for...of` loop (used in the manual approach) is also a special feature. It was introduced in ECMAScript 2015 and provides a concise way to iterate over arrays and other iterable objects. While not strictly necessary for this benchmark, it adds a layer of complexity and potential performance overhead compared to using traditional `for` loops.

**Alternative implementations**

Other alternatives to `Array.from` might include:

* Using the spread operator (`[...src]`) to create an array from an array-like object
* Utilizing `Array.create()` method to create an empty array
* Implementing a custom array creation function using `Buffer.alloc()`, `Uint8Array`, or other low-level data structures

Keep in mind that these alternatives might have different performance characteristics and trade-offs compared to the manual approach.

Overall, this benchmark provides a useful comparison between two common approaches to creating arrays from scratch, highlighting both the benefits and drawbacks of each method.

Related benchmarks:

Array.from vs construct manually (version: 0)

Comparing performance of: Array.from vs manual

Created: 7 years ago by: Guest

Jump to the latest result

Array.from

manual

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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