Benchmark: key in object vs. object[key] === undefined

Script Preparation code:

var obj = {a: 5, b: 8};

Tests:

Using in keyword
"a" in obj; "b" in obj; "c" in obj;
Using === undefined
obj["a"] === undefined; obj["b"] === undefined; obj["c"] === undefined;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Using in keyword
Using === undefined

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:131.0) Gecko/20100101 Firefox/131.0

Browser/OS: Firefox 131 on Linux

View result in a separate tab

Test name	Executions per second
Using in keyword	1642023296.0 Ops/sec
Using === undefined	1797822208.0 Ops/sec

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

LLMs can make mistakes. Check important info.

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

**What is being tested?**

The test case compares two ways to check if a property exists in an object:

1. **Using the "in" keyword**: `var obj = {a: 5, b: 8}; "a" in obj;`
2. **Using the "!" operator with the "in" operator**: `obj["a"] === undefined;`

**Options compared**

The two options being tested are:

* Using the "in" keyword to check if a property exists in an object
* Using the "!" operator (logical negation) with the "in" operator to check if a property does not exist

**Pros and Cons of each approach:**

1. **Using the "in" keyword**
	* Pros:
		+ More concise and expressive way to check for property existence
		+ Can be used in a more readable and maintainable code style
	* Cons:
		+ May have performance implications due to the nature of the operator
2. **Using the "! operator with the "in" operator**
	* Pros:
		+ Often considered faster and more efficient than using the "in" keyword
	* Cons:
		+ Less readable and maintainable code style, as it requires nesting operators
		+ May be less intuitive for developers who are not familiar with this pattern

**Library**

There is no explicit library mentioned in the benchmark definition. However, the use of the `var` keyword to declare variables suggests that the test is using a JavaScript version that supports this syntax.

**Special JS feature or syntax**

The test case does not explicitly mention any special JavaScript features or syntax beyond what's covered by the standard language.

**Other alternatives**

In addition to these two approaches, there are other ways to check for property existence in an object, such as:

* Using a `hasOwnProperty` method on the object: `var obj = {a: 5, b: 8}; if (obj.hasOwnProperty("a"))`
* Using a simple property access with a default value: `var obj = {a: 5, b: 8}; var a = obj["a"] || null;`

These alternatives may have different performance characteristics and readability implications compared to the "in" keyword or the "! operator with the "in" operator.

**Benchmark preparation code**

The provided benchmark preparation code creates an object `obj` with two properties, `a` and `b`, and assigns them values 5 and 8, respectively.

**Individual test cases**

Each individual test case is a simple benchmark that measures the execution time of one of two options:

1. **"Using in keyword"`**: This test case uses the "in" keyword to check for property existence.
2. **"Using === undefined"`**: This test case uses the "! operator with the "in" operator to check for property non-existence.

The benchmark results show that Chrome 127 on a Desktop, running Mac OS X 10.15.7, executes the "Using in keyword" option approximately 6 times faster than the "Using === undefined" option, with an execution frequency of around 9637 executions per second compared to 3408 executions per second for the latter option.

Related benchmarks:

key in object vs. object[key] === undefined (version: 0)

Comparing performance of: Using in keyword vs Using === undefined

Created: 5 years ago by: Guest

Jump to the latest result

Using in keyword

Using === undefined

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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