Benchmark: Array.prototype.concat vs splice for joining two arrays1

Tests:

immutable with concat
var a = [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" , "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello"] var b = [ "hello", "hello", "hello"] var other = a.concat(b)
direct mutation with splice + spread
var a = [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" , "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello"] var b = [ "hello", "hello", "hello"] a.splice(0, 0, ...b);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
immutable with concat
direct mutation with splice + spread

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 dive into the world of MeasureThat.net and explore what's being tested in this benchmark.

**Benchmark Description**

The benchmark measures the performance difference between two approaches for joining two arrays in JavaScript:

1. `concat()`: The `concat()` method creates a new array by concatenating the elements of an existing array with a new array.
2. Direct mutation using `splice()` and the spread operator (`...`): This approach modifies the original array `a` by inserting the elements of `b` at index 0.

**Options being compared**

We have two test cases:

1. **Immutable with concat**: Measures the performance of joining two arrays using `concat()`.
2. **Direct mutation with splice + spread**: Measures the performance of modifying the original array `a` using `splice()` and the spread operator (`...`).

**Pros and Cons**

Here's a brief summary of the pros and cons of each approach:

* **Immutable with concat**:
	+ Pros: No side effects, predictable behavior, easy to reason about.
	+ Cons: Creates a new array, potentially inefficient for large datasets.
* **Direct mutation with splice + spread**:
	+ Pros: Only modifies the original array, potentially more efficient than creating a new one.
	+ Cons: Mutates the original array, can lead to unexpected side effects.

**Library and syntax**

In this benchmark, no specific libraries are used. However, `...` (the spread operator) is used in the second test case, which is a feature introduced in ECMAScript 2015 (ES6).

The spread operator allows you to expand an array into individual elements when passed as an argument to a function or used in an expression.

**Other considerations**

When working with arrays in JavaScript, it's essential to consider the following:

* **Performance**: For large datasets, using `concat()` might be more efficient than modifying the original array.
* **Mutability**: When working with immutable data structures, predictable behavior and easier debugging are often preferred.
* **Side effects**: Be mindful of potential side effects when modifying arrays or other data structures.

**Alternatives**

If you're looking for alternative approaches to join two arrays in JavaScript, consider:

* Using `Array.prototype.push()` and shifting elements: `a = a.concat(b).slice(0);`
* Using `Array.prototype.unshift()` and spreading elements from an array: `a = [...b, ...a];`

Keep in mind that these alternatives may have different performance characteristics and trade-offs compared to the approaches tested in this benchmark.

Related benchmarks:

Array.prototype.concat vs splice for joining two arrays1 (version: 0)

Comparing performance of: immutable with concat vs direct mutation with splice + spread

Created: 6 years ago by: Guest

Jump to the latest result

immutable with concat

direct mutation with splice + spread

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):