Benchmark: Array.prototype.concat vs splice for joining two arrays2

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 = b.concat(a)
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:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.149 Safari/537.36

Browser/OS: Chrome 80 on Mac OS X 10.15.2

View result in a separate tab

Test name	Executions per second
immutable with concat	5457945.0 Ops/sec
direct mutation with splice + spread	4194006.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

The provided benchmark definition json represents two test cases for joining two arrays using different approaches:

1. `Array.prototype.concat` (Test Case 1: "immutable with concat")
2. `splice` with spread operator (`...`) (Test Case 2: "direct mutation with splice + spread")

**Array.prototype.concat**

In this approach, the `concat` method is used to join two arrays. The first array (`a`) is created with a large number of elements, while the second array (`b`) has only a few elements. The `concat` method returns a new array that contains all elements from both arrays.

```javascript
var a = [ ... ]; // long array
var b = [ ... ]; // short array
var result = a.concat(b);
```

**Pros:**

* Simple and straightforward approach.
* No mutation of the original arrays.

**Cons:**

* Creates a new array, which can lead to increased memory usage and garbage collection.
* Not suitable for large datasets or performance-critical applications.

**splice with spread operator**

In this approach, the `splice` method is used to insert elements from the second array (`b`) into the first array (`a`). The `...` operator is used to spread the elements of `b` into the `splice` call.

```javascript
var a = [ ... ]; // long array
a.splice(0, 0, ...b); // insert elements of b into a
```

**Pros:**

* No creation of a new array.
* Suitable for large datasets and performance-critical applications.

**Cons:**

* Mutates the original arrays (`a`).
* Can lead to unexpected behavior if not used carefully (e.g., if `b` is larger than `a`, it will truncate `a`).

**Other alternatives**

1. **Array.prototype.reduce**: You can use the `reduce` method to join two arrays by iterating over each element of one array and concatenating it with the accumulator of the other array.

```javascript
var a = [ ... ];
var b = [ ... ];
var result = a.reduce((acc, curr) => acc.concat(b), []);
```

2. **Array.prototype.forEach**: You can use the `forEach` method to iterate over each element of one array and push it into another array.

```javascript
var a = [ ... ];
var b = [ ... ];
a.forEach(curr => b.push(curr));
```

However, these alternatives may not be as efficient or scalable as using `concat` or `splice` with spread operator for large datasets.

**Library usage**

There is no explicit library usage mentioned in the benchmark definition json. However, if you were to write a custom implementation that uses a third-party library, you might consider using libraries like Lodash or Underscore.js, which provide utility functions for working with arrays and objects.

**Special JS features or syntax**

The benchmark definition does not use any special JavaScript features or syntax (e.g., async/await, Promises, Arrow functions).

Related benchmarks:

Array.prototype.concat vs splice for joining two arrays2 (version: 0)

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

Created: 4 years ago by: Guest

Jump to the latest result

immutable with concat

direct mutation with splice + spread

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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