Let's dive into the world of JavaScript microbenchmarks.

Overview

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided JSON represents a benchmark for three different approaches: _.pickBy (using Lodash), Object.entries + filter, and Object.entries + reduce. Our goal is to understand what's being tested, the pros and cons of each approach, and other considerations.

Benchmark Definition

The benchmark definition is a JavaScript code snippet that sets up an object obj with 1000 properties and fills them with values from 0 to 999. A predicate function predicate is also defined, which checks if a value is even (i.e., v % 2 === 0). The goal is to filter or pick specific properties from the obj based on this predicate.

Approaches

We have three approaches being compared:

1. _.pickBy: Using Lodash's pickBy function, which takes an object and a callback function as arguments. It returns a new object with only the properties that pass the test implemented by the provided function.
2. Object.entries + filter: This approach uses the Array.prototype.filter() method to create a new array with only the elements for which the predicate function returns true. Then, it uses the Object.fromEntries() method to convert the filtered array back into an object.
3. Object.entries + reduce: Similar to the previous approach, but instead of using filter(), we use the Array.prototype.reduce() method to create a new object with only the properties that pass the test implemented by the predicate function.

Pros and Cons

Here's a brief summary of each approach:

• _.pickBy:
  • Pros: Fast and concise, as it relies on Lodash's optimized implementation.
  • Cons: Requires an additional library (Lodash) to be included in the test environment. This might add overhead due to HTTP request latency.
• Object.entries + filter:
  • Pros: Does not require any external libraries, making it a lightweight and self-contained option.
  • Cons: May have higher performance overhead compared to using Lodash's optimized implementation.
• Object.entries + reduce:
  • Pros: Similar to filter(), but with the added benefit of being able to accumulate values in the accumulator object (in case you need to do so).
  • Cons: Also has a potential performance overhead compared to using Lodash's optimized implementation.

Other Considerations

• Performance: The performance differences between these approaches might be negligible for small objects like this one. However, as the size of the object grows, the performance differences may become more pronounced.
• Readability and Maintainability: Using a library like Lodash can make your codebase more readable, but it also adds an extra layer of complexity due to dependencies.

Library: Lodash

Lodash is a popular JavaScript utility library that provides a wide range of functions for tasks such as array manipulation, object transformation, and functional programming. The pickBy function in particular is designed to be fast and efficient while still being easy to use.

Special JS Feature/Syntax

None mentioned explicitly, but note that Object.fromEntries() was introduced in ECMAScript 2015 (ES6) as a part of the standard library. It's a modern feature that allows you to create objects from arrays using a more concise syntax.

Alternatives

If you want to explore other alternatives, here are a few options:

• Array.prototype.filter(): This is a built-in method in JavaScript that creates a new array with only the elements for which the predicate function returns true. However, as mentioned earlier, it might have higher performance overhead compared to using Lodash's optimized implementation.
• Object.keys() + Array.prototype.reduce(): Another approach could be to use Object.keys() to get an array of property names and then use Array.prototype.reduce() to create a new object with only the properties that pass the test implemented by the predicate function.