Benchmark: instanceof String vs typeof string

Script Preparation code:

var strobj = new String("somestring");
var str = "somestring";

Tests:

instanceof
strobj instanceof String
typeof
typeof str === 'string'

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instanceof
typeof

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 23 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and its test cases to understand what's being tested.

**Benchmark Definition**

The benchmark measures the difference in performance between two approaches: `instanceof` and `typeof` checks on JavaScript strings. The code snippet provides an instance of `String` (`strobj`) and a simple string literal (`str`).

**Script Preparation Code**

```javascript
var strobj = new String("somestring");
var str = "somestring";
```

This script creates two variables: `strobj`, which is an instance of the `String` class, and `str`, which is a regular JavaScript string literal.

**Html Preparation Code**

There is no HTML preparation code provided.

**Test Cases**

The benchmark consists of two test cases:

1. `instanceof`
2. `typeof`

These test cases verify that `instanceof String` returns the same result as `typeof str === 'string'`. In other words, they check whether checking if an object is an instance of the `String` class using `instanceof` yields the same result as using the `typeof` operator with a string literal.

**Library and Purpose**

There is no external library used in this benchmark. The `String` class is part of the built-in JavaScript standard library.

**Special JS Features or Syntax**

The benchmark uses the following features:

* **Constructor functions**: In JavaScript, constructors (e.g., `new String()`) create objects that are instances of a particular class.
* **Type checking operators**: The `instanceof` operator and the `typeof` operator with a string literal (`'string'`) perform type checking on JavaScript values.

**Pros and Cons**

Here's a brief summary:

* **`instanceof` approach:**
	+ Pros:
		- Can be more efficient for certain use cases, as it only checks the prototype chain of an object.
		- Allows for more flexibility in implementing custom class hierarchies.
	+ Cons:
		- May be slower than `typeof` in some cases, especially when dealing with large objects or complex prototypes.
* **`typeof` approach:**
	+ Pros:
		- Typically faster and more efficient than `instanceof`, especially for simple types like strings.
		- Simplifies code readability by providing a concise way to check type.
	+ Cons:
		- Limited flexibility when working with custom classes or complex prototypes.

**Other Alternatives**

If you're looking for alternative approaches, consider the following:

* **`String.prototype instanceof`**: This method allows you to check if an object is an instance of `String`, similar to `instanceof`. However, it's less efficient than using `new String()` and may incur additional overhead due to the use of a prototype chain.
* **`Object.prototype.toString.call()`**: This method returns a string representation of an object, which can be used with `=== 'string'` for type checking. While not as concise as `typeof`, it provides more flexibility when working with custom classes.

In summary, the benchmark measures the performance difference between using `instanceof String` and `typeof str === 'string'`. The results help users understand the trade-offs between these approaches in terms of efficiency and readability.

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.64 Safari/537.36

Browser/OS: Chrome 101 on Linux

View result in a separate tab

Test name	Executions per second
instanceof	3761233.5 Ops/sec
typeof	11881618.0 Ops/sec

Related benchmarks:

instanceof String vs typeof string (version: 0)

Comparing performance of: instanceof vs typeof

Created: 2 years ago by: Guest

Jump to the latest result

instanceof

typeof

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 23 days ago):