Benchmark: isArray vs instanceOf vs Symbol.iterator vs Object.prototype.toString.call.slice

Script Preparation code:

var types = {
  array: [1,2,3],
  number: 123,
  string: '123',
  map: new Map([[1,1],[2,2],[3,3]]),
  set: new Set([1,2,3]),
  buffer: new ArrayBuffer([1,2,3]),
  boolean: true,
  arrow: () => {},
  function: function () {},
  object: {},
  u8: new Uint8Array(),
  u16: new Uint16Array(),
  u32: new Uint32Array(),
  i8: new Int8Array(),
  i16: new Int16Array(),
  i32: new Int32Array()
}

var keys = Object.keys(types)

Tests:

isArray
keys.map(key => Array.isArray(types[key]) === true)
instanceof
keys.map(key => (types[key] instanceof Array) === true)
Symbol.iterator
keys.map(key => types[key][Symbol.iterator] !== undefined)
Object.prototype.toString.call
keys.map(key => Object.prototype.toString.call(types[key]).slice(8, -1) == 'Array')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
isArray
instanceof
Symbol.iterator
Object.prototype.toString.call

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks.

**Benchmark Overview**

The provided JSON represents a benchmark test on `MeasureThat.net` that compares four different approaches to check if a value is an array in JavaScript:

1. `Array.isArray()`
2. `instanceof Array`
3. `Symbol.iterator` (also checks for TypedArray, Map, and Set)
4. `Object.prototype.toString.call()` with a slice manipulation

**Options Compared**

Each option is compared using the following test cases:

* `keys.map(key => ... === true)` to check if the condition returns `true` in each case
* The results are then displayed as a raw UA string, which represents the browser's User Agent and version

Here's a brief explanation of each option:

1. **`Array.isArray()`**: This method takes an array-like object (such as a TypedArray, Map, or Set) and returns `true` if it is an actual array.
2. **`instanceof Array```**: This checks if the value is an instance of the `Array` constructor function.
3. **`Symbol.iterator`**: In JavaScript, arrays have a `Symbol.iterator` property that returns an iterator object. Checking for this property (or its presence) can help identify whether a value is an array-like object.
4. **`Object.prototype.toString.call()` with slice manipulation**: This method uses the `toString()` method of the prototype chain to get a string representation of the object, and then uses slicing (`slice(8, -1)`) to extract the type of the object from the string.

**Pros and Cons**

Here's a brief summary of each option:

1. **`Array.isArray()`**:
	* Pros: Simple and efficient.
	* Cons: May return `false` for TypedArrays or other array-like objects that don't have an `array` property.
2. **`instanceof Array```**:
	* Pros: More accurate than `Array.isArray()` for checking if a value is actually an array.
	* Cons: Returns `true` for any object that is a subclass of `Array`, which might not be desirable.
3. **`Symbol.iterator`**:
	* Pros: Covers TypedArrays, Maps, and Sets, in addition to arrays.
	* Cons: May return `false` if the value doesn't have an iterator symbol (although this is rare).
4. **`Object.prototype.toString.call()` with slice manipulation**:
	* Pros: Can cover a wide range of object types by checking the prototype chain.
	* Cons: Slicing and string manipulation can be less efficient than simple checks like `Array.isArray()`.

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.71 Safari/537.36 Edg/94.0.992.38

Browser/OS: Chrome 94 on Windows

View result in a separate tab

Test name	Executions per second
isArray	145145.9 Ops/sec
instanceof	139957.8 Ops/sec
Symbol.iterator	87368.4 Ops/sec
Object.prototype.toString.call	94209.5 Ops/sec

Related benchmarks:

isArray vs instanceOf vs Symbol.iterator vs Object.prototype.toString.call.slice (version: 0)

Symbol.iterator also matches TypedArray, Map, and such

Comparing performance of: isArray vs instanceof vs Symbol.iterator vs Object.prototype.toString.call

Created: 3 years ago by: Guest

Jump to the latest result

isArray

instanceof

Symbol.iterator

Object.prototype.toString.call

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):