Benchmark: Symbol in obj vs obj instanceof constructor

Script Preparation code:

let Sym = Symbol("test")
class test {
  [Sym]
}
let obj = new test

Tests:

Symbol in obj
for (let i = 300; --i;) Sym in obj
obj instanceof constructor
for (let i = 300; --i;) obj instanceof test

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Symbol in obj
obj instanceof constructor

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 15 days ago)

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Mobile Safari/537.36

Browser/OS: Chrome Mobile 131 on Android

View result in a separate tab

Test name	Executions per second
Symbol in obj	9271.8 Ops/sec
obj instanceof constructor	9246.7 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 15 days ago):

LLMs can make mistakes. Check important info.

The benchmark defined in the provided JSON compares two different methods for checking object properties and types in JavaScript:

1. **Using Symbols as Object Properties**
2. **Using `instanceof` for Constructor Checks**

### Comparison of Options

#### 1. Symbol in Object
- **Test Case**: `Sym in obj`
- **Description**: This test checks if a symbol (defined as `Sym`) is a property key in the instance of the `test` class object (`obj`). 
- **Performance**: The benchmark results show that this method has an execution speed of approximately **9271.81 executions per second** in the provided environment.
- **Pros**:
  - Symbols are unique and can prevent property name collisions since each symbol is guaranteed to be unique.
  - They are not enumerable in `for...in` loops or Object.keys(), making them useful for hidden properties.
- **Cons**:
  - Symbols may lead to challenges when checking for properties, as they cannot be easily accessed like string keys unless explicitly referenced.
  - This may add a level of complexity if the code needs to manage or expose symbol properties.

#### 2. `instanceof` Operator
- **Test Case**: `obj instanceof test`
- **Description**: This test checks if the object `obj` is an instance of the `test` class, which is a classic way to verify the type of an object in JavaScript.
- **Performance**: The benchmark results show that this method has an execution speed of approximately **9246.71 executions per second**.
- **Pros**:
  - `instanceof` is easy to read and understand. It clearly signifies type checking against a specific constructor.
  - It works well in inheritance scenarios, allowing identification of an object's lineage reliably.
- **Cons**:
  - The use of `instanceof` can be misleading in contexts involving cross-realm objects (e.g., iframes) which may not share the same reference to the constructor.
  - This method only checks the prototype chain rather than properties directly.

### Performance Considerations
Both methods demonstrate similar performance, with `Symbol in obj` being marginally faster in this case. The choice between the two depends on the specific requirements of a given scenario, including the importance of property encapsulation and type checking.

### Other Alternatives
- **Property Checks with Strings**: A common approach is using string keys and checking properties via `propertyName in obj` or `obj.propertyName`. While simpler, this can lead to name collisions and enumerability issues.
- **Using `Object.hasOwnProperty()`**: This method checks if a property exists on the object itself, preventing issues with inherited properties, but it does not handle Symbols.
- **Using WeakMaps for Private Properties**: Instead of using Symbols, private data can be held in a WeakMap, providing encapsulation without directly exposing the properties.

### Summary
This benchmark illustrates a performance comparison between using symbols for property checking versus the more traditional `instanceof` operator for type checks. Each approach has its own benefits and drawbacks. Developers should consider their specific application needs, including performance requirements and coding style preferences, when choosing between them. Understanding the implications of each method on code readability, maintainability, and performance is crucial in making an informed decision.

Related benchmarks:

Symbol in obj vs obj instanceof constructor (version: 1)

Comparing performance of: Symbol in obj vs obj instanceof constructor

Created: 15 days ago by: Guest

Jump to the latest result

Symbol in obj

obj instanceof constructor

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 15 days ago):