Benchmark: instanceof vs typeof 3

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
test attribute
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
test attribute

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON data to understand what is being tested in this JavaScript microbenchmark.

**Benchmark Definition**

The benchmark definition is represented by the key `"Script Preparation Code"` which contains the initialization code for the test:
```javascript
var obj = {a:2};
```
This code creates an object `obj` with a single property `a` having value 2. This object will be used as the input for various tests.

**Individual Test Cases**

There are four individual test cases, each defined by a unique `"Benchmark Definition"`:
1. `obj instanceof Object `
2. `typeof obj === 'object'`
3. `typeof obj === 'object' && typeof obj !== 'function'`
4. `typeof obj === 'object' && obj.a`

Let's analyze what each test case is checking:

1. **`obj instanceof Object`**: This test checks whether the object `obj` is an instance of the built-in JavaScript type `Object`. In other words, it verifies that `obj` has all the properties and methods of an object.
2. **`typeof obj === 'object'`**: This test checks whether the type of `obj` is exactly `'object'`. Since `obj` is an actual object with properties, this test should pass.
3. **`typeof obj === 'object' && typeof obj !== 'function'`**: This test checks two things:
	* Whether `obj` has a type of `'object'`, which it does.
	* Whether `obj` is not a function (using the `typeof` operator), which it should be since it's an object, not a function.
4. **`typeof obj === 'object' && obj.a`**: This test checks two things:
	* Whether `obj` has a type of `'object'`, which it does.
	* Whether `obj.a` is defined (i.e., whether the property `a` exists on `obj`). Since `obj` was initialized with an `a` property, this test should pass.

**Comparison and Considerations**

The main comparison here is between the three tests that check for the presence of certain properties or types (`instanceof`, `'object'`, and `'object' && !'function'`) versus a test that only checks for the existence of a specific property (`obj.a`).

Pros and cons:

* **`instanceof`**: Pros: precise, informative result. Cons: may not work as expected if `Object.prototype` is modified.
* **Type checking with `typeof`**: Pros: simple, fast, and compatible with most browsers. Cons: does not provide information about property existence or type.
* **`object`-type check combined with property access**: Pros: provides additional information (property existence) while still being relatively fast. Cons: may lead to incorrect results if the property is not defined.

**Library Usage**

There are no explicitly mentioned libraries in the provided benchmark definition, but it's worth noting that some tests might rely on built-in JavaScript features or functions from `Object.prototype` (e.g., `instanceof`).

Related benchmarks:

instanceof vs typeof 3 (version: 0)

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

Created: 5 years ago by: Guest

Jump to the latest result

instanceof

typeof

typeof no function

typeof and test attribute

test attribute

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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