Benchmark: isArray vs instanceof vs typeof

Script Preparation code:

var test = [1,2,3,4];
var c;

Tests:

typeof
if (typeof test === 'object') { c++; }
isArray
if (Array.isArray(test)) { c++; }
instanceof
if (test instanceof Array) { c++; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
typeof
isArray
instanceof

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36

Browser/OS: Chrome 133 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
typeof	13251956.0 Ops/sec
isArray	12989316.0 Ops/sec
instanceof	13220936.0 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark JSON and explain what's being tested.

**Benchmark Definition**

The benchmark is designed to compare three different approaches:

1. `typeof`
2. `Array.isArray`
3. `instanceof`

All three methods are used to check if a variable (`test`) is an object or an array.

**Pros and Cons of each approach:**

* `typeof`: This method checks the type of a variable at runtime, using a special operator in JavaScript. It returns one of the following strings:
	+ `"object"` for objects
	+ `"number"`, `"string"`, etc. for other numeric or string types
	+ `"undefined"` for uninitialized variables
* `Array.isArray`: This method is specifically designed to check if an object is an array, using a static property on the `Array` constructor.
	+ Pros: Efficient and specific to arrays only.
	+ Cons: May return false positives (e.g., checking an object with a numeric property named "0").
* `instanceof`: This method checks if an object is an instance of a particular constructor function. In this case, it's used to check if `test` is an instance of the `Array` constructor.
	+ Pros: More specific than `typeof` and can handle arrays with non-numeric property names.
	+ Cons: May be slower due to the overhead of constructing the `Array` object.

**Library usage**

None of the methods require any external libraries.

**Special JavaScript feature or syntax**

The benchmark uses a special feature of JavaScript called "strict equality" (`===`), which is used to compare values without considering type conversions. This is not explicitly mentioned in the benchmark, but it's implied by using `typeof` and `instanceof`.

**Other alternatives**

There are other ways to check if an object or array in JavaScript:

* Using a regular expression: `test instanceof RegExp.test && test.value === undefined`
* Using the `constructor` property: `test.constructor.name === 'Array'`
* Using a function call with a specific constructor: `new Array(test).length !== 0`

However, these alternatives are not included in this benchmark.

**Benchmark preparation code**

The script preparation code creates an array `test` and assigns it to the variable `c`, which is then used as input for each test case. The `var c;` statement at the end of the script preparation code creates a new variable `c`, which is not referenced anywhere in the benchmark. This is likely done to ensure that the benchmark produces accurate results, even if the variable `c` is not used elsewhere.

**Individual test cases**

Each test case uses one of the three approaches mentioned earlier:

1. `typeof`: Checks if `test` has an `"object"` type.
2. `Array.isArray`: Checks if `test` is a specific instance of the `Array` constructor.
3. `instanceof`: Checks if `test` is an instance of the `Array` constructor.

The benchmark result shows the execution time for each test case in different browsers, with `typeof` performing slightly better than `Array.isArray` and `instanceof`.

Related benchmarks:

isArray vs instanceof vs typeof (version: 0)

Comparing performance of: typeof vs isArray vs instanceof

Created: 3 years ago by: Guest

Jump to the latest result

typeof

isArray

instanceof

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 6 months ago):