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Comparing performance of:
if (test instanceof Array) { c++; } vs if (Array.isArray(test)) { c++; }
Created:
2 years ago
by:
Guest
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Script Preparation code:
var test = [1,2,3,4]; var c;
Tests:
if (test instanceof Array) { c++; }
if (test instanceof Array) { c++; }
if (Array.isArray(test)) { c++; }
if (Array.isArray(test)) { c++; }
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
Previous results
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Test case name
Result
if (test instanceof Array) { c++; }
if (Array.isArray(test)) { c++; }
Fastest:
N/A
Slowest:
N/A
Latest run results:
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's break down the provided benchmark definition and test cases to understand what is being tested. **Benchmark Definition** The benchmark definition is a JSON object that contains the script preparation code, HTML preparation code (which is null in this case), and a brief description of the benchmark. In this case, the script preparation code simply declares an array `test` with some values. The HTML preparation code is not used for this specific benchmark. **Test Cases** There are two test cases: 1. **`if (test instanceof Array) { c++; }`** This test case checks if the value of `c++`, which increments a variable `c`, returns an `Array`. The JavaScript syntax `instanceof` is used to check if an object is an instance of a particular constructor. 2. **`if (Array.isArray(test)) { c++; }`** This test case checks if the value of `c++` returns true when passed to the `Array.isArray()` function, which returns `true` if the input is an array-like object or null. **Comparison** The two test cases are comparing the behavior of JavaScript's built-in functions `instanceof` and `Array.isArray()`. The main difference between these two checks lies in their behavior for non-array-like objects. * `instanceof` will return false even if the value is an array-like object, whereas `Array.isArray()` will return true. * `Array.isArray()` is more permissive but may perform additional work to check if the input has the properties of an array. On the other hand, `instanceof` returns immediately without checking for these properties. **Pros and Cons** * Using `instanceof`: * Pros: More accurate results because it only checks if the value is a direct instance of the specified constructor. * Cons: May not return true for non-array-like objects that have some array-like behavior, such as arrays created using Object.create(). * Using `Array.isArray()`: * Pros: Returns true for both direct instances and most array-like objects, which can be beneficial in certain scenarios. * Cons: May perform additional work to check if the input has the properties of an array. It may not return immediately as required by some tests. **Other Considerations** * In modern JavaScript engines, `Array.isArray()` is generally considered more accurate and safe to use than `instanceof` for checking if a value is an array-like object. * The choice between using `instanceof` and `Array.isArray()` may depend on the specific requirements of the test case. **Library** In this benchmark, there are no external libraries being used. All code is contained within the script preparation code provided in the benchmark definition. **Special JS Features or Syntax** None mentioned. **Alternatives** There are other ways to check if a value is an array-like object: * Using `typeof` operator with equality checks (`if (typeof test === 'object' && !Array.isArray(test) && typeof c++ !== 'undefined')`) * Checking for the presence of certain properties on the object (`if (Object.prototype.hasOwnProperty.call(test, 'length'))`) * Using a third-party library like Lodash's `isArrayLike()` function Keep in mind that these alternatives may not be as straightforward or efficient as using `Array.isArray()`.
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