Benchmark: Update Or Insert - splice vs slice

Script Preparation code:

var list = [];
for (var i = 0; i < 1000 * 1000; i++) {
    list.push({ id: i, name: `${i}` });
}

var updates = [
  { id: (1000 * 1000) - 1, name: 'Changed' },
  { id: (1000 * 1000) + 1, name: 'Added' },
];

function updateOrInsertBySplice(
  array,
  update,
  key,
) {
  const index = array.findIndex(item => item[key] === update[key])
  const startIndex = index === -1 ? 0 : index
  const toRemove = Number(index !== -1)
  return array.splice(startIndex, toRemove, update)
}

function updateOrInsertBySlice(
  array,
  update,
  key,
) {
  const index = array.findIndex(item => item[key] === update[key])
  const startIndex = index === -1 ? 0 : index
  const toRemove = +Boolean(index !== -1)
  return [...array.slice(0, startIndex), update, ...array.slice(startIndex + toRemove)]
}

Tests:

splice
updates.forEach(update => updateOrInsertBySplice(list, update, 'id'))
slice
updates.forEach(update => updateOrInsertBySlice(list, update, 'id'))

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
splice
slice

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

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**Overview**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided JSON data represents a benchmark test case, which compares two approaches for updating or inserting elements into an array: `splice` and `slice`. In this explanation, we'll break down what's being tested, the pros and cons of each approach, and other considerations.

**Benchmark Definition**

The benchmark definition is represented by the `Script Preparation Code` section in the JSON data. It creates a sample list with 1 million elements, populates it with random data, and defines two functions: `updateOrInsertBySplice` and `updateOrInsertBySlice`. The latter function takes an array, an update object, and a key as arguments.

**What's being tested**

The test case measures the performance of two approaches:

1. **`splice`**: This approach uses the `splice` method to replace elements in the array. It finds the index of the element with the matching key, removes the existing element, and inserts the new element at that position.
2. **`slice`**: This approach uses the `slice` method to create a copy of the array up to the index of the element with the matching key, appends the update object to the copied array, and then concatenates the two parts.

**Pros and Cons**

*   **`splice`**:
    *   Pros: Efficient for small arrays or when updating multiple elements. The `splice` method is optimized for insertion and deletion operations.
    *   Cons: Inefficient for large arrays, as it requires shifting all subsequent elements to fill the gap created by the removed element. This can lead to poor performance in such cases.
*   **`slice`**:
    *   Pros: Efficient for large arrays or when updating a single element. The `slice` method creates a new array without modifying the original, which avoids unnecessary shifts and copying of elements.
    *   Cons: Less efficient than `splice` for small arrays or when updating multiple elements, as it requires creating an additional copy of the array.

**Other Considerations**

*   **Browser behavior**: MeasureThat.net runs tests on various browsers to provide a fair comparison. The provided benchmark result shows that Chrome 114 performs better with both approaches.
*   **Device platform**: The test is run on a desktop device, which might affect performance compared to mobile devices or other platforms.

**Library and Special JS Features**

The `slice` method uses the built-in JavaScript function of the same name. This function creates a shallow copy of an array segment by extracting a specified number of elements from the string's current position to its end.

No special JavaScript features are mentioned in this benchmark.

**Alternatives**

In JavaScript, other methods for updating or inserting elements into arrays could be considered:

*   **`Array.prototype.map()`**: This method creates a new array with transformed values and does not modify the original array. However, it may require more memory due to the creation of an additional array.
*   **`Array.prototype.filter()`**: Similar to `map()`, this method creates a new array with filtered values but does not support insertion.
*   **Custom loops or recursion**: While these approaches might avoid built-in functions like `splice` and `slice`, they are generally less efficient due to the overhead of explicit control structures.

Related benchmarks:

Update Or Insert - splice vs slice (version: 0)

Comparing performance of: splice vs slice

Created: 2 years ago by: Guest

Jump to the latest result

splice

slice

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):