Benchmark: instanceof vs typeof 2

Script Preparation code:

var obj = {a:2};

Tests:

instanceof
obj instanceof Object
typeof
typeof obj === 'object'
typeof no function
typeof obj === 'object' && typeof obj !== 'function'
typeof obj or string
typeof obj === 'object' && typeof obj === 'string'
new Ojb
Object(obj) == obj

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof
typeof
typeof no function
typeof obj or string
new Ojb

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 16 days ago):

LLMs can make mistakes. Check important info.

The benchmark you've provided tests different methods for determining the type or instance of a JavaScript object. This is particularly relevant in JavaScript, where types can sometimes be less predictable due to its dynamic nature. Below, I’ll explain each approach tested in the benchmark, the pros and cons of each, and other considerations.

### Options Compared

1. **`obj instanceof Object`**
   - **Test Name**: `instanceof`
   - **Description**: This checks if `obj` is an instance of `Object`. 
   - **Execution Speed**: Very low in this benchmark.
   - **Pros**:
     - It's a clear and semantic way to determine if an object is derived from a particular prototype.
   - **Cons**:
     - Can be slower than other type-checking methods.
     - Will return false for objects created from a different realm (like iframes or workers), which can be a limitation in certain situations.

2. **`typeof obj === 'object'`**
   - **Test Name**: `typeof`
   - **Description**: This checks if `obj` is of type 'object'. 
   - **Execution Speed**: Fastest in this benchmark.
   - **Pros**:
     - Very fast and simple; directly checks the type as reported by the JavaScript engine.
   - **Cons**:
     - It returns true for arrays and `null` (since `typeof null` is also 'object'), which might be misleading.

3. **`typeof obj === 'object' && typeof obj !== 'function'`**
   - **Test Name**: `typeof no function`
   - **Description**: This further refines the check to exclude functions.
   - **Execution Speed**: Slower than just `typeof`.
   - **Pros**:
     - Eliminates functions from the results, providing a clearer distinction.
   - **Cons**:
     - Still returns true for arrays and `null`.

4. **`typeof obj === 'object' && typeof obj === 'string'`**
   - **Test Name**: `typeof obj or string`
   - **Description**: This is logically flawed as it checks if `obj` is both 'object' and 'string' at the same time, which can never be true.
   - **Execution Speed**: Relatively slow and should be avoided because it makes no logical sense.
   - **Pros**: 
     - None, as it will always evaluate to false.
   - **Cons**:
     - Confusing logic that may mislead developers.

5. **`Object(obj) == obj`**
   - **Test Name**: `new Ojb` (note the typo; should be `new Obj`).
   - **Description**: This checks if wrapping `obj` with `Object()` gives back the same reference.
   - **Execution Speed**: Moderate speed.
   - **Pros**:
     - Provides insight into object created versus primitive wrappers.
   - **Cons**:
     - Could lead to unexpected results when working with primitives, and it's less concise than the other methods.

### Summary of Benchmark Results

From the benchmark results, `typeof obj === 'object'` is the fastest method, followed by the check using `Object(obj)`. The `instanceof` check was the slowest among the provided methods.

### Other Alternatives

Other alternatives could include:

- **`Array.isArray(obj)`**: Specifically checks if an object is an array, addressing some of the ambiguities presented by `typeof`.
- **`Object.prototype.toString.call(obj)`**: This returns a string representation of the type, and can differentiate between objects, arrays, and primitives.
- **Custom Type Guards**: In TypeScript, developers might create custom type guard functions to offer more refined type checking when creating complex applications.

### Conclusion

The benchmark effectively demonstrates the performance differences and logical implications of using type checking methods in JavaScript. For performance-sensitive code, using `typeof` is usually preferred unless specific instance checks are necessary. Developers should choose the method that best fits their needs and consider the nuances of each approach.

Latest run results:

Run details: (Test run date: 17 days ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:133.0) Gecko/20100101 Firefox/133.0

Browser/OS: Firefox 133 on Linux

View result in a separate tab

Test name	Executions per second
instanceof	128272848.0 Ops/sec
typeof	1442049664.0 Ops/sec
typeof no function	722150528.0 Ops/sec
typeof obj or string	715871360.0 Ops/sec
new Ojb	1160713984.0 Ops/sec

Related benchmarks:

instanceof vs typeof 2 (version: 1)

Comparing performance of: instanceof vs typeof vs typeof no function vs typeof obj or string vs new Ojb

Created: 17 days ago by: Guest

Jump to the latest result

instanceof

typeof

typeof no function

typeof obj or string

new Ojb

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 16 days ago):