Benchmark: Array isArray vs typeof (negative case)

Script Preparation code:

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

Tests:

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

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

isArray

105.0M/s

typeof

101.7M/s

View exact numbers

✓ isArray: 105,023,952 ops/sec
• typeof: 101,713,664 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
typeof
isArray

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 11 months ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36

Browser/OS: Chrome 138 on Mac OS X 10.15.7

View result in a separate tab

typeof

101.7M/s

isArray

87.2M/s

View exact numbers

Test name	Executions per second
✓ typeof	101,713,664 Ops/sec
isArray	87,162,336 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

LLMs can make mistakes. Check important info.

The benchmark provided tests the performance of two different methods for determining if a variable is an array in JavaScript: using `typeof` and using the static method `Array.isArray()`. Below, we will explore what each approach involves, their pros and cons, and other considerations.

### Benchmark Overview

**1. Test Cases:**
   - **Test Name: `typeof`**
     - Benchmark Definition: `if (typeof test === 'object') { c++; }`
   - **Test Name: `isArray`**
     - Benchmark Definition: `if (Array.isArray(test)) { c++; }`

### Options Compared

- **`typeof` Operator:**
  - **Description:** The `typeof` operator in JavaScript returns a string indicating the type of the unevaluated operand. Here, it is used to check if `test` is of the type 'object'. Since arrays are technically a type of object in JavaScript, this check may return true for arrays.
  
- **`Array.isArray()` Method:**
  - **Description:** `Array.isArray()` is a static method that returns `true` if the argument passed to it is an array, and `false` otherwise. This method is specifically designed to check for arrays and is generally more reliable than using `typeof`.

### Pros and Cons

- **Using `typeof`:**
  - **Pros:**
    - Quick and straightforward syntax.
    - Works with fewer lines of code.
  - **Cons:**
    - Can produce false positives: It returns true for any object, not just arrays. For example, it will return `true` for objects, dates, and other non-array objects.
  
- **Using `Array.isArray()`:**
  - **Pros:**
    - Specifically checks for arrays, providing more accurate results.
    - Only returns `true` for arrays, eliminating false positives.
  - **Cons:**
    - Introduced in ECMAScript 5, which may not be supported in very old environments or browsers.
    - Slightly more verbose than using `typeof`.

### Performance Considerations

Based on the benchmark results:

- **Execution Speed:**
  - `typeof` achieved approximately **74,057,608 executions per second**.
  - `Array.isArray()` achieved approximately **72,110,464 executions per second**.
  
In this specific context, `typeof` performs slightly better than `Array.isArray()`. However, the performance difference may be negligible in most real-world applications, and the choice may be based more on correctness rather than benchmark speed.

### Alternatives

There are other methods to check if a variable is an array including:

1. **Instanceof Operator:**
   - Example: `if (test instanceof Array) { c++; }`
   - **Pros:** Checks if `test` is an instance of the Array constructor.
   - **Cons:** Can fail if the code is running in different execution contexts (e.g., iframes) because each context may have its own Array object.

2. **Object.prototype.toString.call:**
   - Example: `if (Object.prototype.toString.call(test) === '[object Array]') { c++; }`
   - **Pros:** Works in all contexts and provides reliable results across different environments.
   - **Cons:** More complex syntax, lower readability for those unfamiliar with the method.

### Conclusion

When determining if a variable is an array in JavaScript, both `typeof` and `Array.isArray()` have their use cases. While `typeof` may offer slightly better performance in this benchmark, `Array.isArray()` is the preferred method for accurately identifying arrays without the risk of false positives. Depending on the specific needs of your project—especially with regard to compatibility and correctness—using `Array.isArray()` is often the better choice. Additionally, understanding alternative methods can help cater to specific project requirements or environments.

Array isArray vs typeof (negative case) (version: 1)

Comparing performance of: `typeof vs isArray`

Created: one year ago by: Guest

Go to the latest result

typeof

isArray

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

Array isArray vs typeof (negative case) (version: 1)

Comparing performance of: typeof vs isArray

Created: one year ago by: Guest

Go to the latest result

typeof

isArray

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

Related benchmarks

Comparing performance of: `typeof vs isArray`