Benchmark: Function: typeof vs instanceof

Script Preparation code:

const f = () => {};
let i = 0;

Tests:

instanceof
if (f instanceof Function) i++;
typeof
if (typeof f === 'function') i++

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof
typeof

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36 Edg/133.0.0.0

Browser/OS: Chrome 133 on Windows

View result in a separate tab

Test name	Executions per second
instanceof	36468924.0 Ops/sec
typeof	37488652.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark and explain what's being tested, the pros and cons of each approach, and other considerations.

**Benchmark Overview**

The benchmark is designed to compare two approaches for checking if an object is a function in JavaScript: `instanceof` and `typeof`.

**Test Cases**

There are two test cases:

1. **`instanceof`**: The benchmark checks if the value of `f instanceof Function` is truthy.
2. **`typeof`**: The benchmark checks if the result of `typeof f` is `'function'`.

**Options Compared**

The two options being compared are:

* Using `instanceof` to check if an object is a function
* Using `typeof` with the `=== 'function'` comparison operator to check if an object is a function

**Pros and Cons of Each Approach**

1. **`instanceof`**:
	* Pros:
		+ More precise, as it checks if the prototype chain of the object includes Function.
		+ Can be useful in certain situations where `typeof` might return `'object'` instead of `'function'`.
	* Cons:
		+ May be slower due to the overhead of checking the prototype chain.
2. **`typeof`**:
	* Pros:
		+ Faster, as it only checks the type of the object without evaluating its prototype chain.
		+ Often used in everyday JavaScript development.
	* Cons:
		+ Might return `'object'` instead of `'function'`, which could lead to incorrect results.

**Other Considerations**

* **Library Usage**: Neither test case uses any external libraries, so it's a bare-metal comparison of the two approaches.
* **JavaScript Features**: The benchmark does not use any special JavaScript features or syntax that might affect the results.

**Alternative Approaches**

If you were to add more test cases, you could consider other methods for checking if an object is a function, such as:

* Using `Function()` constructor: `new Function() === f`
* Using `Object.getPrototypeOf()`: `Object.getPrototypeOf(f) === Function.prototype`

Keep in mind that these alternative approaches might have different trade-offs in terms of performance and precision.

In summary, the benchmark compares two common methods for checking if an object is a function in JavaScript: `instanceof` and `typeof`. While both have their pros and cons, `typeof` is generally faster but may return incorrect results in certain situations.

Related benchmarks:

Function: typeof vs instanceof (version: 0)

Comparing performance of: instanceof vs typeof

Created: 8 years ago by: Guest

Jump to the latest result

instanceof

typeof

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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