Benchmark: Array.prototype.concat vs spread operator

Script Preparation code:

var array1 = Array(400).fill().map(() => Math.round(Math.random() * 40));
var array2 = Array(400).fill().map(() => Math.round(Math.random() * 40));

Tests:

Array.prototype.concat
var others = array1.concat(array2);
spread operator
var others = [...array1, ...array2];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array.prototype.concat
spread operator

Fastest: N/A

Slowest: N/A

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Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):

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Let's break down what's happening in this benchmark.

**Benchmark Description**

The benchmark is comparing two ways to concatenate (merge) two arrays (`array1` and `array2`) with 400 elements each:

1. **Array.prototype.concat**: Using the traditional `concat()` method, which is a part of JavaScript's Array prototype.
2. **Spread Operator**: Using the new ES6 spread operator (`[...]`) to merge the two arrays.

**Library**

No libraries are being used in this benchmark.

**Special JS Features or Syntax**

* The benchmark uses the spread operator (`[...]`), which was introduced in ECMAScript 2015 (ES6).
* The benchmark also uses `Array(400).fill().map(() => Math.round(Math.random() * 40))`, which is a concise way to create an array of 400 elements, each containing a random number between 0 and 39.

**Options Compared**

The two options being compared are:

1. **Array.prototype.concat**: Using the `concat()` method to merge the two arrays.
2. **Spread Operator**: Using the spread operator (`[...]`) to merge the two arrays.

**Pros and Cons**

Here's a brief summary of each approach:

### Array.prototype.concat

* **Pros**:
	+ Widely supported in older browsers.
	+ Easy to read and understand.
* **Cons**:
	+ Can be slower than the spread operator for large arrays.
	+ May have performance issues with deep array nesting.

### Spread Operator

* **Pros**:
	+ Faster than `concat()` for large arrays.
	+ More concise and expressive code.
	+ Well-supported in modern browsers and Node.js environments.
* **Cons**:
	+ Not supported in older browsers (pre-ES6).
	+ May have performance issues with very deep array nesting.

**Other Considerations**

When deciding between these two approaches, consider the following:

* If you need to support older browsers or a specific legacy environment, use `Array.prototype.concat`.
* For modern environments and large arrays, prefer the spread operator for its performance benefits.
* If you're working on a project that requires strict ES6+ compliance, use the spread operator.

**Other Alternatives**

There are other ways to concatenate arrays in JavaScript, such as using the `forEach()` method or manual looping. However, these approaches are generally less efficient than `concat()` and the spread operator for large arrays.

For example:

* Using `forEach()`:
```javascript
var others = [];
array1.forEach(function (item) {
  others.push(item);
});
array2.forEach(function (item) {
  others.push(item);
});
```

These alternatives should be avoided unless you have specific requirements or constraints that necessitate their use.

Related benchmarks:

Array.prototype.concat vs spread operator (version: 0)

Compare the new ES6 spread operator with the traditional concat() method

Comparing performance of: Array.prototype.concat vs spread operator

Created: 8 years ago by: Guest

Jump to the latest result

Array.prototype.concat

spread operator

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model llama3.1:latest, generated one year ago):