Benchmark Overview

The benchmark titled "Array.prototype.slice vs spread operator large arrays" aims to compare the performance of two methods for copying large arrays in JavaScript: the traditional Array.prototype.slice() method and the modern ES6 spread operator ([...]).

Test Cases Description

1. Test Case: Array.prototype.slice large

   • Benchmark Definition:

     var params = Array.from({length: 10000}, () => 1);
     var other = params.slice();
     

   • Explanation: This test case creates a large array (params) filled with 10,000 elements, all set to 1. It then uses the slice() method to create a shallow copy of that array (other). The slice() method is well-established in JavaScript and allows for copying parts of an array. When called without arguments, it copies the entire array.

2. Test Case: spread operator large

   • Benchmark Definition:

     var params = Array.from({length: 10000}, () => 1);
     var other = [ ...params ];
     

   • Explanation: Similarly, this test also creates an array with 10,000 elements of 1. However, it uses the spread operator ([...]) to create a new array. The spread operator is a concise syntax introduced in ES6 that allows for the expansion of elements from an iterable (in this case, the array params) into a new array.

Performance Results

The results indicate the Executions Per Second for each test. Here are the numbers from the benchmark:

• Array.prototype.slice large: 3606.10 executions per second
• Spread operator large: 3586.52 executions per second

Pros and Cons

Array.prototype.slice

Pros:

• Compatibility: It is widely supported in all JavaScript environments, including older versions, making it a safe choice for projects that need to support legacy browsers.
• Clarity: Some developers may find it easier to understand and maintain, especially if they are not familiar with the ES6 syntax.

Cons:

• Verbosity: Slightly longer syntax, which may contribute to reduced readability in larger contexts.
• Performance: In some instances (depending on the environment), it may be less performant compared to the spread operator.

Spread Operator

Pros:

• Conciseness: The spread syntax is cleaner and easier to read, making the code more expressive.
• New Features: It allows for merging or interpolating arrays and objects in an elegant fashion.

Cons:

• Browser Support: While most modern browsers support the spread operator, legacy browsers may not, which is a consideration for projects that need extensive compatibility.
• Slightly Higher Overhead: In certain scenarios and with very large datasets, the spread operator might introduce a bit more overhead in performance compared to slice().

Other Considerations

• Memory Consumption: Both techniques create a shallow copy of the array, meaning that if the array contains references to objects, those objects will not be duplicated; only the references will be copied.
• Use Cases: Choosing between the two can depend on the specific use case. For copying entire arrays, both methods work well, but understanding the nuances in performance and readability might help in making a decision.

Alternatives

Other alternatives for copying arrays in JavaScript include:

• Array.from(): This method can also be used to create a new array instance from an existing array-like or iterable object.

  var other = Array.from(params);
  

• Concat Method: Using the concat() method to copy an array by combining it with an empty array:

  var other = [].concat(params);
  

Each of these methods (like Array.from and concat) has its pros and cons regarding performance and readability as well. Ultimately, the choice depends on the specific scenario, codebase requirements, and developer preferences.