Benchmark: Iterate through a large object

Script Preparation code:

window.obj = {};
for (let i = 0; i < 10000; i++) {
  obj[`p${i}`] = Math.random();
}
delete obj.p0;

Tests:

for in
for (const key in obj) { window.result = obj[key]; }
keys
const keys = Object.keys(obj); for (let i = 0; i < keys.length; i++) { window.result = obj[keys[i]]; }
getOwnPropertyNames
const keys = Object.getOwnPropertyNames(obj); for (let i = 0; i < keys.length; i++) { window.result = obj[keys[i]]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for in
keys
getOwnPropertyNames

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36

Browser/OS: Chrome 95 on Mac OS X 10.14.6

View result in a separate tab

Test name	Executions per second
for in	206.7 Ops/sec
keys	208.3 Ops/sec
getOwnPropertyNames	184.2 Ops/sec

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

LLMs can make mistakes. Check important info.

**Benchmark Overview**

The provided JSON represents a JavaScript microbenchmark, specifically designed to measure the performance of three different approaches for iterating through an object: `for in`, `Object.keys()`, and `Object.getOwnPropertyNames()`.

**What is tested?**

In this benchmark, 3 test cases are compared:

1. **Iterating through an object using `for in`**: This approach iterates over all enumerable properties of the object.
2. **Iterating through an object using `Object.keys()`**: This approach uses the `keys()` method to get an array of all own property names (enabling us to use a for loop).
3. **Iterating through an object using `Object.getOwnPropertyNames()`**: This approach uses the `getOwnPropertyNames()` method, which returns an array containing all property names that are directly accessible on the object.

**Options compared**

The three test cases aim to measure how efficiently each approach can iterate over the object's properties and access their values.

**Pros and Cons of each approach:**

1. **`for in`**: This is a legacy way of iterating over objects, as it also iterates over non-enumerable properties (e.g., those inherited from the prototype chain). It's generally slower than using `Object.keys()` or `getOwnPropertyNames()`, which are more efficient.
2. **`Object.keys()` and `Object.getOwnPropertyNames()`**: These two methods provide a safe way to iterate over object properties without accessing non-enumerable ones. The choice between them depends on whether you want to include inherited properties (using `Object.keys()`) or not (using `getOwnPropertyNames()`).
3. **Cons of `for in`:** Iterates over both enumerable and non-enumerable properties, which can lead to unexpected behavior if you don't control the prototype chain.

4. **Pros of `Object.keys()` and `getOwnPropertyNames():`**
   - Faster than `for in`.
   - Provide a safe way to iterate over object properties.
   - Can be used with loops (like for).

5. **Cons of `Object.keys()` and `getOwnPropertyNames()`:** 
   - May not include inherited properties if using `getOwnPropertyNames()`, which could lead to missing some values.
   - Could have performance overhead due to extra operations performed by the method.

**Special JS feature or syntax**

In this benchmark, no special JavaScript features or syntax are used beyond standard ECMAScript. The only notable syntax is the use of template literals (`\r\n obj[`p${i}`] = Math.random();`) in the script preparation code.

Related benchmarks:

Iterate through a large object (version: 0)

Note that this doesn't work with non-enumerable properties.

Comparing performance of: for in vs keys vs getOwnPropertyNames

Created: 6 years ago by: Registered User

Jump to the latest result

for in

keys

getOwnPropertyNames

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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