Benchmark: conditional self-assignment vs. membership check

Tests:

if condition
const x = { foo: [] }; const keys = Array.from({length: 5000}).map((x, i) => i < 2500 ? i : i - 2500); for (const key of keys) { if (!Object.prototype.hasOwnProperty.call(x, key)) { x[key] = []; } }
self-assignment
const x = { foo: [] }; const keys = Array.from({length: 5000}).map((x, i) => i < 2500 ? i : i - 2500); for (const key of keys) { x[key] = x[key] ?? []; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
if condition
self-assignment

Fastest: N/A

Slowest: N/A

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

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

**Benchmark Overview**

The benchmark consists of two test cases, each designed to measure the performance difference between two approaches:

1. **Membership Check (if condition)**: This approach uses an `if` statement to check if a key exists in the object.
2. **Self-Assignment**: This approach uses the nullish coalescing operator (`??`) to assign an empty array to the non-existent key.

**Options Being Compared**

The benchmark is comparing the performance of these two approaches:

1. **Membership Check (if condition)**: This method involves checking if a key exists in the object using `Object.prototype.hasOwnProperty.call(x, key)`. If the key doesn't exist, it creates a new property with an empty array value.
2. **Self-Assignment**: This method uses the nullish coalescing operator (`??`) to assign an empty array to the non-existent key. The expression `x[key] ?? []` returns an empty array if `x[key]` is undefined or null, and assigns it to the property.

**Pros and Cons of Each Approach**

1. **Membership Check (if condition)**:
	* Pros: This approach is more explicit and easier to understand for developers who are familiar with traditional JavaScript.
	* Cons: It may lead to slower performance due to the additional check and potential array creation.
2. **Self-Assignment**:
	* Pros: This approach is concise, efficient, and can lead to better cache locality since it only assigns a new value if the key doesn't exist.
	* Cons: The nullish coalescing operator is a relatively recent addition to JavaScript (introduced in ECMAScript 2020), and some developers might not be familiar with it.

**Library Used**

There is no explicit library used in this benchmark. However, it's worth noting that the `Object.prototype.hasOwnProperty.call()` method is an intrinsic part of the JavaScript object prototype chain.

**Special JS Features or Syntax**

The nullish coalescing operator (`??`) is a feature introduced in ECMAScript 2020. It's used to provide a concise way to handle null and undefined values in expressions.

**Other Alternatives**

If you're interested in exploring other approaches, here are a few alternatives:

1. **Using `in` operator**: Instead of using `Object.prototype.hasOwnProperty.call()`, you can use the `in` operator to check if a key exists in an object.
```javascript
if (key in x) {
  // key exists, perform action
}
```
2. **Using a simple assignment with default value**: You can assign a default value to the non-existent key using the syntax:
```javascript
x[key] = []; // or x[key] = null, undefined, etc.
```
Keep in mind that these alternatives may not be as efficient or concise as the original approaches.

I hope this explanation helps you understand the benchmark and its test cases!

Related benchmarks:

conditional self-assignment vs. membership check (version: 0)

Comparing performance of: if condition vs self-assignment

Created: 2 years ago by: Guest

Jump to the latest result

if condition

self-assignment

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):