Benchmark: Rest parameters - MeasureThat.net

Script Preparation code:

function assertEqual(v1, v2) {
  if (v1 instanceof Array && v2 instanceof Array) {
    if (v1.length != v2.length) return false;
    for (var i = 0; i < v1.length; i++)
      if (!assertEqual(v1[i], v2[i])) return false;
    return true;
  }
  return v1 === v2;
}

Tests:

ES5 copy arguments
function unary(val) { if (arguments.length !== 1) { var $a=new Array(arguments.length); for (var $i=0;$i<arguments.length;$i++) { $a[$i]=arguments[$i]; } throw $a; } return true; } try { unary(1, 2, 3, 4, true, false, "a", "b"); } catch (e) { assertEqual(e, [1, 2, 3, 4, true, false, "a", "b"]); }
ES6 copy rest
function unary(val, ...extra) { if ((val === void 0) || extra.length > 0) { throw [val, ...extra]; } return true; } try { unary(1, 2, 3, 4, true, false, "a", "b"); } catch (e) { assertEqual(e, [1, 2, 3, 4, true, false, "a", "b"]); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
ES5 copy arguments
ES6 copy rest

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 provided benchmark and explain what is being tested, compared, and their pros/cons.

**Benchmark Definition**

The benchmark definition represents a JavaScript function that tests the behavior of two different approaches to handling rest parameters in JavaScript functions.

1. **ES5 copy arguments**: This approach uses an array to copy the arguments from the `unary` function call.
```javascript
function unary(val, ...extra) {
  if ((val === void 0) || extra.length > 0) {
    throw [val, ...extra];
  }
  return true;
}
```
The test case creates a new array with the same number of elements as the `extra` parameter and throws an error if the length is not equal.

2. **ES6 copy rest**: This approach uses the rest syntax (`...`) to capture the arguments from the `unary` function call.
```javascript
function unary(val, ...extra) {
  if ((val === void 0) || extra.length > 0) {
    throw [val, ...extra];
  }
  return true;
}
```
The test case uses the rest syntax to capture the arguments and throws an error if there are any.

**Comparison**

Both approaches aim to detect when a function call has more than one argument beyond the first. The difference lies in how they handle this scenario:

1. **ES5 copy arguments**: This approach explicitly copies the arguments into an array, which can lead to performance overhead due to the creation of an extra data structure.
2. **ES6 copy rest**: This approach uses the rest syntax to capture the arguments, which is more concise and likely to be optimized by the JavaScript engine.

**Pros/Cons**

1. **ES5 copy arguments**:
	* Pros: More explicit and potentially easier to understand for developers familiar with arrays.
	* Cons: May lead to performance overhead due to array creation.
2. **ES6 copy rest**:
	* Pros: Concise, optimized by the JavaScript engine, and more modern syntax.
	* Cons: May be less clear to developers without experience with rest parameters.

**Other Considerations**

Both approaches assume that a function call with no arguments beyond the first should behave differently from one with multiple arguments. This assumption may not hold true in all cases, such as when using `arguments` object directly or with certain types of functions (e.g., arrow functions).

**Alternatives**

If you need to detect when a function call has more than one argument beyond the first, you could consider alternative approaches:

1. **Using `arguments.length > 1`**: This approach is simple and direct but may not work correctly in all scenarios.
```javascript
function unary(val, ...extra) {
  if (arguments.length > 1) {
    // handle extra arguments
  }
  return true;
}
```
Keep in mind that this approach relies on the `arguments` object being available and may not work as expected in certain contexts.

In conclusion, the ES5 copy arguments and ES6 copy rest approaches are compared to determine which one is more efficient and suitable for handling rest parameters. The choice ultimately depends on your specific use case, performance requirements, and personal preference.

Related benchmarks:

Rest parameters (version: 0)

Comparing performance of: ES5 copy arguments vs ES6 copy rest

Created: 9 years ago by: Guest

Jump to the latest result

ES5 copy arguments

ES6 copy rest

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):