Benchmark: Object key access vs array index access

Script Preparation code:

var items = Array.from(
  Array(1000),
  (item, index) => ({ key: index, value: index*10 })
);
var objContainer = new Object();
var arrContainer = new Array(items.length);

// For a tenth of the number of items...
for (let i = items.length/10; i >= 0; i--) {
  // Choose a random item
  const index = Math.floor(Math.random() * items.length);
  const item = items[index];

  // Assign the item to the object and array containers
  objContainer[item.key] = item;
  arrContainer[item.key] = item;
}

Tests:

Object key access
items.forEach((item) => objContainer[item.key]?.value)
Array index access
items.forEach((item) => arrContainer[item.key]?.value)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Object key access
Array index access

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 27 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Safari/537.36 Edg/132.0.0.0

Browser/OS: Chrome 132 on Windows

View result in a separate tab

Test name	Executions per second
Object key access	57410.4 Ops/sec
Array index access	56666.0 Ops/sec

Autogenerated LLM Summary (model gemma2:9b, generated 6 months ago):

LLMs can make mistakes. Check important info.

This benchmark compares the performance of accessing items using object keys versus array indices in JavaScript.

**Options Compared:**

* **Object key access:**  Using bracket notation (`objContainer[item.key]`) to retrieve values from an object.
* **Array index access:** Directly accessing elements using their numerical index (`arrContainer[item.key]`).

**Pros and Cons:**

* **Object Key Access:**
    * **Pros:** More flexible as keys can be any data type (strings, numbers, objects). Easier to organize data with meaningful identifiers.
    * **Cons:** Can be slower than array indexing due to potential hash table lookups. 
* **Array Index Access:**
    * **Pros:** Generally faster because elements are stored contiguously in memory. Direct access using indices is very efficient.
    * **Cons:** Less flexible, keys must be numerical and sequential.  Less intuitive for representing real-world data relationships.

**Considerations:**

* **Data Structure Choice:**  The choice depends on your data. If you need flexibility and meaningful identifiers, use objects. If you have a fixed set of items with numerical relationships, arrays are better.
* **Performance Trade-offs:** In most cases, the performance difference between these two approaches is negligible unless dealing with very large datasets.

**Other Alternatives:**

* **Maps:**  Similar to objects but provide faster lookups due to hash table implementation. Useful when you need efficient key-value storage and retrieval.

Let me know if you have any other questions!

Related benchmarks:

Object key access vs array index access (version: 0)

Tests the speed of accessing an item by object key vs array index.

Comparing performance of: Object key access vs Array index access

Created: 3 years ago by: Registered User

Jump to the latest result

Object key access

Array index access

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gemma2:9b, generated 6 months ago):