Benchmark: "In" vs "Undefined" property access

Tests:

In
const foo = {} const a = 'status' in foo ? 1 : 0; const b = 'dog' in foo ? 0 : 1; const c = 'shaggy' in foo ? 2 : 1; const d = 'the' in foo ? 100000 : 10323;
property access
const foo = {} const a = foo.status ? 1 : 0; const b = foo.dog ? 0 : 1; const c = foo.shaggy ? 2 : 1; const d = foo.the ? 100000 : 10323;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
In
property access

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's break down the benchmark and explain what's being tested, compared, and some pros/cons of different approaches.

**Benchmark Overview**

The benchmark is comparing two ways to access properties in JavaScript: using the `in` operator and direct property access (e.g., `foo.status`). The test cases are designed to demonstrate the difference in performance between these two approaches.

**Test Cases**

There are two test cases:

1. **"In"` Test Case:
```javascript
const foo = {}
const a = 'status' in foo ? 1 : 0;
const b = 'dog' in foo ? 0 : 1;
const c = 'shaggy' in foo ? 2 : 1;
const d = 'the' in foo ? 100000 : 10323;
```
In this test case, the `in` operator is used to check if a property exists in the object `foo`. If the property exists, the corresponding value is assigned to the variable.

2. **"Property Access"` Test Case:
```javascript
const foo = {}
const a = foo.status ? 1 : 0;
const b = foo.dog ? 0 : 1;
const c = foo.shaggy ? 2 : 1;
const d = foo.the ? 100000 : 10323;
```
In this test case, the object `foo` is accessed directly using its properties (e.g., `foo.status`). If the property exists, the corresponding value is assigned to the variable.

**Comparison**

The benchmark compares the performance of these two approaches:

1. **"In"` Test Case: Uses the `in` operator to check if a property exists in the object.
2. **"Property Access"` Test Case: Directly accesses the properties of the object.

**Pros/Cons and Considerations**

Here are some pros and cons of each approach, as well as considerations:

1. **"In"` Operator:
	* Pros:
		+ Efficient when checking if a property exists (e.g., in a large dataset).
		+ Can be faster than direct property access.
	* Cons:
		+ May be slower for simple property accesses, as it involves a lookup.
2. **Direct Property Access**:
	* Pros:
		+ Faster for simple property accesses, as it directly accesses the value.
	* Cons:
		+ May lead to performance issues if the object is large or complex.

In general, the `in` operator is suitable when:

* You need to check if a property exists in an object (e.g., iterating over properties).
* The object is large and you want to optimize lookup times.

Direct property access is suitable when:

* You directly access a simple property value.
* You prioritize performance for small objects or datasets.

**Libraries and Special Features**

None of the test cases use any external libraries. However, it's worth noting that some JavaScript engines may have specific optimizations or behaviors for certain syntax features (e.g., `in` operator). But in this benchmark, these nuances are not exploited.

**Alternatives**

Other alternatives to consider:

1. **Object hasOwnProperty()**: Instead of using the `in` operator, you can use the `hasOwnProperty()` method to check if a property exists in an object.
```javascript
const foo = {}
console.log(foo.hasOwnProperty('status')) // true or false
```
2. **Brute force approach**: You can also brute-force check for property existence by accessing each property and checking if it's defined.
```javascript
const foo = {}
for (let key in foo) {
  if (foo.hasOwnProperty(key)) {
    // property exists
  }
}
```
However, these alternatives are not typically used in production code, as they may be slower than the `in` operator or direct property access.

**Benchmark Results**

The latest benchmark results show that:

* The "Property Access" test case outperforms the "In" test case.
* Mobile Safari 14 on iOS 14.0 executes both tests cases at around 330 million executions per second.

Related benchmarks:

"In" vs "Undefined" property access (version: 0)

Comparing performance of: In vs property access

Created: 5 years ago by: Guest

Jump to the latest result

In

property access

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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