Benchmark: Object key access vs array index access bigger

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; 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: one year ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser/OS: Chrome 131 on Linux

View result in a separate tab

Test name	Executions per second
Object key access	453708.8 Ops/sec
Array index access	460607.1 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

LLMs can make mistakes. Check important info.

The benchmark defined in the JSON tests the performance of two data access methods in JavaScript: accessing values in an object using an object key versus accessing values in an array using an index. This benchmark is particularly relevant for software engineers interested in understanding the performance implications of different data structures in JavaScript.

### Comparisons Made
1. **Object Key Access**: 
   - **Benchmark Code**: `items.forEach((item) => objContainer[item.key]?.value)`
   - This accesses the value of each object stored in `objContainer` through its key. The `?.` is the optional chaining operator, which safely accesses `value` without throwing an error if `objContainer[item.key]` is `undefined`.

2. **Array Index Access**: 
   - **Benchmark Code**: `items.forEach((item) => arrContainer[item.key]?.value)`
   - In this approach, the code accesses array elements at the index specified by `item.key`. The technique leverages the structure of `arrContainer`, treated as an array.

### Pros and Cons of Each Approach

**Object Key Access Pros**:
- **Flexibility**: Objects can store key-value pairs where keys can be strings or symbols, making them more suitable for non-numeric keys.
- **Sparse Data**: They can efficiently represent sparse collections since you can omit keys that do not have an associated value without wasting space.

**Object Key Access Cons**:
- **Performance**: Generally slower than array access, especially when accessed through non-integer keys, as it involves hash table lookups rather than continuous memory access.

**Array Index Access Pros**:
- **Performance**: Faster for numerical indices since JavaScript engines optimize array access. Arrays are stored in contiguous memory locations, which can significantly improve access speed.
- **Simplicity**: If you're indexing directly, the syntax is cleaner and represents a more straightforward access method.

**Array Index Access Cons**:
- **Limited Keying**: Arrays are generally intended for numerical indexing only. Using them as a key-value storage can be inappropriate for applications requiring more complex structures.
- **Maintenance**: Potential issues with managing gaps or undefined values if keys are not continuous indices.

### Considerations
When choosing between object key access and array index access, consider:
- **Data Structure Intent**: Use an object for key-value mappings where key types may vary, and use arrays for ordered data collections with numeric indices.
- **Performance Needs**: If performance is critical, as seen in the benchmark results where array access is marginally faster, you may prefer array structures for high-frequency access patterns.

### Alternatives
1. **Maps**: For key-value storage where keys can be any type and have more predictable insertion and retrieval performance than objects—especially when storing many elements.
2. **Sets**: If you're dealing with collections where uniqueness is essential, which doesn't directly map to the benchmark but is useful in JavaScript contexts.
3. **WeakMaps and WeakSets**: For memory-efficient collections that allow garbage collection for objects that no longer have references.

In summary, the benchmark effectively demonstrates the performance difference between two fundamental data access methods in JavaScript. It highlights the speed advantages of array access while also noting the flexible nature of objects. Understanding these differences helps in selecting the appropriate data structure based on specific requirements and performance needs.

Related benchmarks:

Object key access vs array index access bigger (version: 1)

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

Comparing performance of: Object key access vs Array index access

Created: one year ago by: Guest

Jump to the latest result

Object key access

Array index access

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):