Benchmark: Checking for presence of object key

Script Preparation code:

var obj = {
   'first' : 1,
   'is' : 1,
   'some' : 1,
   'nice' : 1,
   'test' : 1,
   'last' : 1
}

Tests:

in – first element
if ('first' in obj) { }
in – last element
if ('last' in obj) { }
typeof – first element
if (typeof obj['first'] !== "undefined") { }
typeof – last element
if (typeof obj['last'] !== "undefined") { }
! – first element
if (!obj['first']) { }
! – last element
if (!obj['last']) { }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
in – first element
in – last element
typeof – first element
typeof – last element
! – first element
! – last element

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Safari/537.36

Browser/OS: Chrome 132 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
in – first element	165426208.0 Ops/sec
in – last element	167101968.0 Ops/sec
typeof – first element	167672080.0 Ops/sec
typeof – last element	159355472.0 Ops/sec
! – first element	165898624.0 Ops/sec
! – last element	176808656.0 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

I'll break down the provided benchmark definition and test cases for you.

**Benchmark Definition**

The provided JSON represents a JavaScript microbenchmark that tests the performance of different approaches to check if an object key exists or is defined.

The `Script Preparation Code` sets up an example object `obj` with multiple properties, including some keys ("first", "is", "some", etc.) and some non-existent keys ("last").

**Options Compared**

There are six test cases that compare the performance of different approaches:

1. **in** operator (e.g., `'first' in obj`)
2. **typeof** operator with a check for `undefined` (e.g., `typeof obj['first'] !== "undefined"`)
3. **!** operator with a negation (e.g., `!obj['first']`)
4. `in` operator on the last element of an array (not explicitly mentioned in the provided test cases, but implied)
5. `typeof` operator with a check for `undefined` on the last element of an array
6. Negation of the existence of a key (similar to `!obj['first']`, but without using the `!` operator)

**Pros and Cons**

Here's a brief summary of each approach:

1. **in** operator:
	* Pros: Simple, intuitive, and widely supported.
	* Cons: Can be slower due to the need for a string comparison and potential lookup in a hash table.
2. **typeof** operator with `undefined` check:
	* Pros: Can be faster since it avoids the string comparison and only checks if the property exists in the object.
	* Cons: May not work as expected if the property is not defined but has another value (e.g., `null` or an empty string).
3. **!** operator with negation:
	* Pros: Simple and concise, but may be slower than other approaches due to the need for a boolean comparison.
	* Cons: May lead to false negatives if the property is not defined.
4. **in** operator on the last element of an array (not explicitly tested in the provided benchmark):
	* Pros: Fast since it only checks if the property exists in the object, without performing any additional operations.
	* Cons: Not explicitly tested in this benchmark.

**Libraries and Special JS Features**

None of the test cases use a specific library. However, the `typeof` operator is used to check for undefined values, which is a built-in JavaScript feature.

No special JavaScript features are mentioned or used in the provided benchmark.

**Other Alternatives**

If you're looking for alternative approaches to check if an object key exists, here are some options:

* Using a simple boolean flag variable: `let hasKey = 'first' in obj;`
* Checking if the property is defined using `in` operator on the `Object.keys()` method: `'first' in Object.keys(obj)`
* Using a library like Lodash's `hasIn()` function.

Keep in mind that these alternatives might have performance implications or additional complexity, depending on your specific use case.

Related benchmarks:

Checking for presence of object key (version: 0)

Comparing performance of: in – first element vs in – last element vs typeof – first element vs typeof – last element vs ! – first element vs ! – last element

Created: 7 years ago by: Guest

Jump to the latest result

in – first element

in – last element

typeof – first element

typeof – last element

! – first element

! – last element

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):