Benchmark: self-assignment vs. if condition

Tests:

if condition
const x = { foo: [] }; const keys = ["foo", "bar"]; for (const key of keys) { if (!Object.prototype.hasOwnProperty.call(x, key)) { x[key] = []; } }
self-assignment
const x = { foo: [] }; const keys = ["foo", "bar"]; 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

Latest run results:

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

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I'd be happy to explain the benchmark and its results.

**Benchmark Description**

The benchmark measures the performance difference between two approaches: using an `if` condition to check for property existence, and using self-assignment (`x[key] = x[key] ?? []`) to initialize missing properties in an object.

**Options Compared**

The two options being compared are:

1. **If Condition**: This approach checks if a property exists on the object `x` before assigning a new value to it.
2. **Self-Assignment**: This approach uses the nullish coalescing operator (`??`) to assign an empty array to missing properties in a single statement.

**Pros and Cons of Each Approach**

1. **If Condition**:
	* Pros: Clear and explicit code, easy to understand and maintain.
	* Cons: May incur additional overhead due to the check.
2. **Self-Assignment**:
	* Pros: More concise and efficient code, can be faster since it only involves a single assignment.
	* Cons: May require more expertise to understand and maintain, as the nullish coalescing operator is a relatively new feature.

**Library and Purpose**

Neither of these approaches relies on any external libraries. However, they do utilize some built-in JavaScript features:

1. **`Object.prototype.hasOwnProperty.call()`**: This method checks if an object has a certain property.
2. **Nullish Coalescing Operator (`??`)**: This operator returns the first operand if it's not null or undefined; otherwise, it returns the second operand.

**Special JS Feature**

The self-assignment approach uses the nullish coalescing operator (`??`), which is a relatively recent feature introduced in ECMAScript 2020. This operator allows for concise way to handle null or undefined values.

**Other Considerations**

When writing performance-critical code, it's essential to consider the trade-offs between readability, maintainability, and execution speed. In this case, the self-assignment approach is likely to be faster since it involves a single statement, whereas the `if` condition approach may incur additional overhead due to the check.

**Alternatives**

If you don't want to use JavaScript's nullish coalescing operator or if you prefer an even more concise approach, you can consider using the following alternatives:

1. **Using `in` operator**: Instead of `Object.prototype.hasOwnProperty.call()`, you can use the `in` operator to check if a property exists in the object.
```javascript
for (const key of keys) {
  x[key] = Array.isArray(x[key]) ? [] : [];
}
```
2. **Using spread operator (`...`)**: You can use the spread operator to initialize missing properties with an empty array.
```javascript
for (const key of keys) {
  x[key] = [...x[key], []];
}
```
However, these alternatives may have different performance characteristics and may not be as concise or readable as the self-assignment approach.

Related benchmarks:

self-assignment vs. if condition (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):