Benchmark: instanceof vs typeof

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 and test attribute
typeof obj === 'object' && obj.a

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof
typeof
typeof no function
typeof and test attribute

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one month ago):

LLMs can make mistakes. Check important info.

**What is being tested?**

The provided JSON represents a JavaScript microbenchmark that tests the performance of three different approaches to check if an object is an instance of a specific type or has a certain property.

In more detail, the benchmark compares the following:

1. `obj instanceof Object`: Checks if the object `obj` is an instance of the `Object` constructor.
2. `typeof obj === 'object'`: Uses the `typeof` operator to check if the type of `obj` is `'object'`.
3. `typeof obj === 'object' && typeof obj !== 'function'`: Combines checks from both 1 and 2, ensuring `obj` is an object but not a function.
4. `typeof obj === 'object' && obj.a`: Similar to the previous one, but also checks if `obj` has a property named `a`.

These approaches aim to evaluate the performance difference in checking object types or properties.

**Pros and Cons of each approach:**

1. **`obj instanceof Object`**: This approach is more accurate for checking if an object is of a specific type (in this case, `Object`). However, it may be slower due to the constructor call.
2. **`typeof obj === 'object'`**: This method is faster but less accurate, as it only checks the type of the object and does not account for its properties or prototype chain.
3. **`typeof obj === 'object' && typeof obj !== 'function'`**: This approach combines both speed and accuracy by checking the type and then verifying the absence of a function property. It's likely the fastest and most accurate option.
4. **`typeof obj === 'object' && obj.a`**: Similar to the previous one, but also checks if `obj` has a property named `a`. This approach is likely slower due to the additional check.

**Library usage**

There are no external libraries used in this benchmark. The tests only rely on built-in JavaScript features.

**Special JS feature or syntax**

None mentioned explicitly in the provided information. If present, it would be essential to note and discuss its relevance to the benchmark's results.

**Other alternatives**

Alternative approaches to check object types or properties include:

* Using a library like Lodash (`_.isPlainObject`, `_.isObject`) or Prototype Chain methods (`instanceof` with `Object.prototype.toString()`)
* Utilizing ES6 classes and instance checks
* Implementing custom getters or accessor functions

Keep in mind that each approach may have its trade-offs regarding performance, accuracy, and maintainability.

**Benchmark preparation code**

The provided script creates an object `obj` with a single property `a`. This simple object serves as the test subject for the benchmark's various checks.

In the context of this microbenchmark, these approaches are being compared to evaluate their relative performance on modern JavaScript engines.

Latest run results:

Run details: (Test run date: 2 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36

Browser/OS: Chrome 130 on Windows

View result in a separate tab

Test name	Executions per second
instanceof	6454089.0 Ops/sec
typeof	10082723.0 Ops/sec
typeof no function	5265486.5 Ops/sec
typeof and test attribute	5388014.5 Ops/sec

Related benchmarks:

instanceof vs typeof (version: 0)

Comparing performance of: instanceof vs typeof vs typeof no function vs typeof and test attribute

Created: 4 years ago by: Guest

Jump to the latest result

instanceof

typeof

typeof no function

typeof and test attribute

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one month ago):