Benchmark: Spread first vs map first then Array.from

HTML Preparation code:

<!--your preparation HTML code goes here-->

Script Preparation code:

let foo = new Map();
for (let i = 0; i < 1_000_000; i++) {
  foo.set(i, i % 8);
}

Tests:

Spread first then map
[...foo.entries()].map(([i, iMod8]) => [i, iMod8.toString()])
Map first then Array.from
Array.from(foo.entries().map(([i, iMod8]) => [i, iMod8.toString()]))

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Spread first then map
Map first then Array.from

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one month ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:136.0) Gecko/20100101 Firefox/136.0

Browser/OS: Firefox 136 on Mac OS X 10.15

View result in a separate tab

Test name	Executions per second
Spread first then map	23.2 Ops/sec
Map first then Array.from	12.5 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one month ago):

LLMs can make mistakes. Check important info.

The benchmark defined in the provided JSON compares two approaches for transforming entries from a `Map` in JavaScript. Specifically, it evaluates the performance of:

1. **Spread first then map** - transforming the entries of the `Map` into an array using the spread operator (`[...]`) and then applying `map()` to convert the entries into strings.
2. **Map first then `Array.from`** - mapping the entries of the `Map` to strings first and then using `Array.from()` to create an array from the mapped iterable.

### Breakdown of the Test Cases:

1. **Spread first then map**
   - **Benchmark Definition**: `[...foo.entries()].map(([i, iMod8]) => [i, iMod8.toString()])`
   - **Test Name**: "Spread first then map"
   - This approach uses the spread operator to expand the entries of the `Map` into a new array, and then it uses the `map()` function to transform each entry from a tuple `[i, iMod8]` into a new tuple where `iMod8` is converted to a string.

2. **Map first then Array.from**
   - **Benchmark Definition**: `Array.from(foo.entries().map(([i, iMod8]) => [i, iMod8.toString()]))`
   - **Test Name**: "Map first then Array.from"
   - In this case, the `map()` function is applied directly to the entries of the `Map`, transforming them into string representations. The `Array.from()` function is then used to create a new array from the iterable returned by `map()`.

### Performance Results:

- "Spread first then map": Approximately 23.21 executions per second.
- "Map first then Array.from": Approximately 12.50 executions per second.

### Pros and Cons:

#### Spread First then Map
- **Pros**:
  - The spread operator is typically more straightforward and easier to read, indicating that we're converting an entire iterable to an array in one clear step.
  - Since the entire `Map` is already expanded to an array, `map()` operates directly on an array, which can sometimes lead to optimizations by the JavaScript engine.
- **Cons**:
  - If the dataset is significantly large, creating a new array with the spread operator could be less memory efficient, as it creates an intermediate array.

#### Map First then Array.from
- **Pros**:
  - This method may reduce the memory overhead by deferring the array creation until after the mapping, especially useful in scenarios where only some entries might be required.
  - Encourages the use of lazy evaluation; mapping might be more efficient for large data sets.
- **Cons**:
  - The need to use `Array.from()` could add an additional step that makes the code slightly less readable to those unfamiliar with `Array.from()`.
  - As shown by the benchmark results, this approach is slower in performance in this specific test case compared to using the spread operator first.

### Other Considerations:
- **Readability**: While performance is a crucial consideration, the readability and maintainability of code should also be factored into decision-making. The first approach may appeal more to developers due to its clarity.
- **Optimization**: JavaScript engines have optimizations that can vary between operations like `map()` and the spread operator. What is faster might not be consistent across environments or even versions of the same engine.
  
### Alternatives:
- **Using `forEach` instead of `map`**: For cases where side effects are needed and a new array is not the primary goal, you could use `forEach()`.
- **Manual Looping**: One could also use a `for...of` loop to manually iterate over the entries, providing further custom optimization but sacrificing the conciseness and expressiveness of functional programming styles.
- **Other Libraries**: For more complex transformations, using libraries like **Lodash** or **Underscore.js** might provide additional utility functions that could further optimize performance or improve code readability.

In summary, this benchmark is assessing the overhead and performance differences between two common strategy patterns for data transformation in JavaScript using Maps. Understanding these differences provides insights into performance trade-offs, ease of maintenance, and optimal coding practices.

Related benchmarks:

Spread first vs map first then Array.from (version: 1)

Comparing performance of: Spread first then map vs Map first then Array.from

Created: one month ago by: Guest

Jump to the latest result

Spread first then map

Map first then Array.from

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one month ago):