Benchmark: for-in with hasOwnProperty checking vs object.keys

Script Preparation code:

var obj = {
  'a': 1,
  'b': 1,
  'c': 1,
  'd': 1,
  'e': 1,
  'f': 1,
  'g': 1
};

Tests:

for-in
for (var i=10000; i > 0; i--) { for (var key in obj) { if ({}.hasOwnProperty(obj, key)) { console.log(key); } } }
Object.keys
for (var i=10000; i > 0; i--) { Object.keys(obj).forEach(key => console.log(key)); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
Object.keys

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):

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

**Benchmark Overview**

The benchmark compares two approaches to iterate over an object in JavaScript: using `for-in` with a check for `hasOwnProperty`, and using `Object.keys`.

**Options Compared**

The two options are:

1. **For-in with hasOwnProperty checking**: This approach uses the `for-in` loop, which iterates over an object's properties using their property names as strings. The `hasOwnProperty` method is used to check if a property belongs to the object.
2. **Object.keys**: This approach uses the `Object.keys()` method, which returns an array of a given object's own enumerable property names.

**Pros and Cons**

**For-in with hasOwnProperty checking:**

Pros:

* More explicit control over iteration
* Can be useful for iterating over objects that may have inherited properties from a prototype chain

Cons:

* Slower performance compared to `Object.keys`
* Can lead to unexpected behavior if not used carefully (e.g., when dealing with prototype chains)

**Object.keys:**

Pros:

* Faster performance compared to `for-in` with `hasOwnProperty` checking
* More concise and expressive code

Cons:

* Less explicit control over iteration
* May not work as expected for objects that have inherited properties from a prototype chain

**Other Considerations**

* The benchmark is run in Firefox 85 on a Linux desktop, which may affect the results.
* The `var` keyword is used in both options, which can lead to variable hoisting and other issues in older browsers.

**Library and Special JS Feature**

There are no external libraries being used in this benchmark. However, the `for-in` loop uses a special JavaScript feature called "property iteration," which allows iterating over an object's properties using their property names as strings.

**Benchmark Preparation Code**

The preparation code creates an object `obj` with 10 properties ( `'a'` to `'j'`) and assigns each property a value of 1. This object is used for both test cases.

**Individual Test Cases**

Each test case defines a separate benchmark that measures the performance of one of the two options. The first test case uses the `for-in` loop with a check for `hasOwnProperty`, while the second test case uses `Object.keys`.

The latest benchmark results show that the `Object.keys` approach is significantly faster than the `for-in` with `hasOwnProperty` checking approach.

**Alternatives**

Other approaches to iterate over an object in JavaScript include:

* Using `forEach()` or `map()`
* Using a `while` loop
* Using a library like Lodash's `iteratee()`

However, these alternatives may have different performance characteristics and trade-offs compared to the options being tested.

Related benchmarks:

for-in with hasOwnProperty checking vs object.keys (version: 0)

Comparing performance of: for-in vs Object.keys

Created: 5 years ago by: Guest

Jump to the latest result

for-in

Object.keys

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):