Benchmark: Symbol in obj vs obj instanceof constructor 3

Script Preparation code:

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

Tests:

Symbol in obj
for (let i = 30000; --i;) {Sym in obj; Sym in []}
obj instanceof constructor
for (let i = 30000; --i;) {obj instanceof test; [] 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: 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
Symbol in obj	49.6 Ops/sec
obj instanceof constructor	50.8 Ops/sec

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

LLMs can make mistakes. Check important info.

This benchmark tests the performance differences between two ways of checking property existence and instance membership in JavaScript, specifically between using `Symbol in obj` and `obj instanceof constructor`.

### Benchmark Overview

1. **Symbol in obj**
   - **Test Case**: `for (let i = 30000; --i;) {Sym in obj; Sym in []}`
   - **Purpose**: This test measures how efficiently JavaScript can check if a property (in this case, a symbol) exists in an object. The symbol `Sym` is added to an instance of the class `test` with a symbolic key.
   - **Execution Context**: The test dynamically checks the presence of `Sym` in `obj` (an instance of the class) and in an empty array (which won't have the symbol).

2. **obj instanceof constructor**
   - **Test Case**: `for (let i = 30000; --i;) {obj instanceof test; [] instanceof test}`
   - **Purpose**: This test measures how efficiently JavaScript can check whether an object is an instance of a particular class (in this case, if `obj` is an instance of the class `test`).
   - **Execution Context**: Similar to the first, this loop checks if `obj` is an instance of the class `test` and whether an empty array `[]` is an instance of `test`, which it will not be.

### Performance Results Summary

The results from the benchmark run indicate that the execution of `obj instanceof test` yielded a higher execution rate (approximately 50.75 executions per second) compared to `Sym in obj`, which had about 49.60 executions per second. This suggests that checking for an instance via the `instanceof` operator may be slightly more performant on the tested platform.

### Pros and Cons

**Using `Sym in obj`:**
- **Pros**:
  - Symbols provide a unique and non-collision way to create properties in objects, making it safer in multi-module systems.
  - Checking for the presence of a property using `in` can be straightforward and easy to understand.
  
- **Cons**:
  - The performance may be lower compared to `instanceof` for this specific benchmark.
  - Non-standard and may create confusion if the purpose of using symbols is not well understood by all team members.

**Using `obj instanceof constructor`:**
- **Pros**:
  - Generally very fast as it checks the prototype chain directly.
  - Easy to understand and universally applicable for checking object types.

- **Cons**:
  - Less flexibility compared to using symbols; it’s strictly for checking instances of a class.
  - Can lead to issues in complex inheritance hierarchies or with multiple inheritance scenarios where prototype chains can be convoluted.

### Other Considerations and Alternatives

1. **Alternative Checks**:
   - Using `Object.prototype.hasOwnProperty.call(obj, 'propertyName')` for standard property checks would allow checking for own properties and avoid prototype chain issues but wouldn't work with symbols.
   - Use the newer `Object.hasOwn()` method which provides similar functionality to `hasOwnProperty()` but with better semantics (and can be more performant).
  
2. **When to Use Each**:
   - Use symbols when you want to define properties that will not conflict with other properties or that you want to keep hidden from typical iteration.
   - Use `instanceof` for type-checking when you're working with class instances or built-in types, as it's clear and readable.

In conclusion, the results provide insight into the performance characteristics of checking for property existence using symbols versus type checking with `instanceof`, helping developers make informed decisions about which approach to adopt based on their specific use cases.

Related benchmarks:

Symbol in obj vs obj instanceof constructor 3 (version: 1)

Comparing performance of: Symbol in obj vs obj instanceof constructor

Created: one year ago by: Guest

Jump to the latest result

Symbol in obj

obj instanceof constructor

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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