Benchmark: object keys vs loop

Script Preparation code:

var a = [{"id":7,"h":76},{"id":4,"h":34},{"id":9,"h":89}];
var d = [];

Tests:

fori
for(var i=0;i<a.length;i++)d.push(a[i].id);
forin
for(var i in a)d.push(i.id);
foreach
a.forEach((i)=>d.push(i.id));
backwhile
var i = a.length; while(--i)d.push(a[i].id);
cache4
var z = a.length; for(var i=0;i<z;i++)d.push(a[i].id);
4of
for(var i of a)d.push(i.id);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
fori
forin
foreach
backwhile
cache4
4of

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

Let's dive into the benchmark and explain what's being tested, compared, and their pros/cons.

**Benchmark Definition**

The provided JSON represents a JavaScript microbenchmarking framework called MeasureThat.net. The benchmark is defined by two parts:

1. **Script Preparation Code**: This code sets up the test data, which in this case is an array `a` containing objects with `id` and `h` properties.
2. **Benchmark Definition**: This is a string that defines the JavaScript loop used to iterate over the array elements and push their `id` values into another array `d`. There are four different loops implemented:
	* `for(var i=0;i<a.length;i++)d.push(a[i].id);`
	* `for(var i in a)d.push(i.id);`
	* `a.forEach((i)=>d.push(i.id));`
	* `var i = a.length; while(--i)d.push(a[i].id);`
	* `for(var i=0;i<z;i++)d.push(a[i].id);` (cache4)
	* `for(var i of a)d.push(i.id);` (4of)

**Comparison**

The benchmark compares the performance of these four different loop implementations. Each test case has its own unique characteristics, which we'll discuss below.

**Loop Implementations and Their Characteristics**

1. **Classic `for` loop**: `for(var i=0;i<a.length;i++)d.push(a[i].id);`
	* Pros: Easy to understand and implement, straightforward logic.
	* Cons: Can be slower than other methods due to the overhead of incrementing `i`.
2. **For...in loop**: `for(var i in a)d.push(i.id);`
	* Pros: Uses the iterator's implicit conversion to string, which can improve performance for some use cases.
	* Cons: May not work as expected if the array has non-numeric properties or if the iteration is performed on an object with enumerable properties.
3. **`forEach` loop**: `a.forEach((i)=>d.push(i.id));`
	* Pros: Uses a native method, which can be faster and more memory-efficient than traditional loops.
	* Cons: May not work in older browsers that don't support `forEach`, and the callback function's implicit conversion to string can lead to performance issues for large datasets.
4. **Cache-based loop**: `var i = a.length; while(--i)d.push(a[i].id);`
	* Pros: Can be faster than traditional loops by reusing the iterator's value, which reduces the overhead of incrementing `i`.
	* Cons: May not work correctly for arrays with sparse or non-contiguous elements.
5. **Cached index loop**: `for(var i=0;i<z;i++)d.push(a[i].id);` (cache4)
	* Pros: Similar to the cache-based loop, but uses a cached variable to avoid incrementing `i`.
	* Cons: May not work correctly for arrays with sparse or non-contiguous elements.

**Library Usage**

None of the loops use any external libraries.

**Special JS Features**

There are no special JavaScript features used in this benchmark. However, some modern JavaScript engines (like V8) have features like just-in-time compilation and incremental execution that can affect performance. MeasureThat.net uses a custom interpreter to run these tests on various JavaScript engines.

**Other Considerations**

* The `z` variable in the cache4 loop is not defined anywhere, which means this test case may be incorrect or incomplete.
* Some browsers (like Chrome) might have issues with executing `forEach` loops when the iterator's value is an object property, like in the for...in loop.

**Alternatives**

Other JavaScript engines and benchmarking frameworks exist, such as:

* V8 Microbenchmark Suite
* jsPerf
* Benchmark.js
* JSHint

Each of these tools has its own strengths and weaknesses, but MeasureThat.net is a popular choice among developers due to its simplicity and ease of use.

Related benchmarks:

object keys vs loop (version: 0)

Comparing performance of: fori vs forin vs foreach vs backwhile vs cache4 vs 4of

Created: 9 years ago by: Guest

Jump to the latest result

fori

forin

foreach

backwhile

cache4

4of

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):