Benchmark: How to reduce an object to a sub-object fast

Script Preparation code:

var source = {
  a: 0,
  b: 1,
  c: 2,
  d: 3,
  e: 4,
  f: 5,
  various: null
}

var select = ['a', 'b', 'c', 'd', 'e', 'f']

var selectReduceAssign = () =>
  select.reduce(
    (accumulator, current) =>
      Object.assign(accumulator, { [current]: source[current] }),
    {}
  )

var selectReduceSpread = () =>
  select.reduce(
    (accumulator, current) =>
      ({ ...accumulator, [current]: source[current] }),
    {}
  )

var selectReduceAddExplicitly = () =>
  select.reduce(
    (accumulator, current) =>
    {
      accumulator[current] = source[current]
      return accumulator
    },
    {}
  )

var selectPick = ({ a, b, c, d, e, f }) => ({ a, b, c, d, e, f })

Tests:

selectReduceAssign
selectReduceAssign()
selectReduceSpread
selectReduceSpread()
selectReduceAddExplicitly
selectReduceAddExplicitly()
selectPick
selectPick(source)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
selectReduceAssign
selectReduceSpread
selectReduceAddExplicitly
selectPick

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/116.0

Browser/OS: Firefox 116 on Windows

View result in a separate tab

Test name	Executions per second
selectReduceAssign	2213031.2 Ops/sec
selectReduceSpread	1871661.5 Ops/sec
selectReduceAddExplicitly	6851319.5 Ops/sec
selectPick	98379576.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark definition and test cases to understand what is being tested.

**Benchmark Definition:**
The benchmark measures how fast it can reduce an object (in this case, `source`) to a sub-object by selecting specific properties (`a`, `b`, `c`, `d`, `e`, and `f`) and assigning their values to the resulting sub-object. The approach used is a reduction function applied to an array of selected indices.

**Test Cases:**

1. `selectReduceAssign()`: This test case uses the `reduce()` method with an initial accumulator value of `{}` and assigns each property from `source` to the accumulator object using `Object.assign()`. The callback function returns the updated accumulator.
2. `selectReduceSpread()`: Similar to the previous test, but it uses the spread operator (`{ ...accumulator, [current]: source[current] }`) instead of `Object.assign()` to assign properties to the accumulator object.
3. `selectReduceAddExplicitly()`: This test case uses a more explicit approach by assigning each property value directly to the accumulator object using `{ accumulator[current] = source[current]; return accumulator; }`.
4. `selectPick(source)`: This test case is different from the others, as it does not use any reduction function or loop. Instead, it simply returns an object with the selected properties (`a`, `b`, `c`, `d`, `e`, and `f`) using a simple object literal.

**Library/Techniques:**

* `Object.assign()`: A method that assigns enumerable own properties from one or more specified values to an object.
* Spread operator (`{ ...accumulator, [current]: source[current] }`): A syntax feature introduced in ECMAScript 2015 (ES6) that allows creating a new object by spreading the properties of an existing object.

**Special JS Features/Syntax:**

* The use of spread operator is a notable example of ES6 syntax being used in this benchmark.
* `Object.assign()` is a standard JavaScript method, but its usage might be less common due to its simplicity and the existence of more modern alternatives like the spread operator.

**Pros and Cons of each approach:**

1. `selectReduceAssign()`:
	* Pros: Concise and easy to understand.
	* Cons: May have performance issues if `Object.assign()` is called frequently, as it creates a new object each time.
2. `selectReduceSpread()`: 
	* Pros: More readable and efficient than `Object.assign()`, as it avoids creating intermediate objects.
	* Cons: Requires ES6 support for the spread operator.
3. `selectReduceAddExplicitly()`:
	* Pros: Explicit and easy to understand, with minimal performance overhead.
	* Cons: May be less concise and more verbose than other approaches.

**Other Alternatives:**

1. Using `reduce()` with a custom callback function that directly assigns properties to the accumulator object without using `Object.assign()` or spread operator.
2. Utilizing libraries like Lodash or other utility functions for array manipulation and object creation.
3. Employing more modern JavaScript features, such as `Object.fromEntries()` or `Object.assign` alternatives like `Array.prototype.forEach()` with an index mapping.

In conclusion, the choice of approach depends on personal preference, performance considerations, and the desired level of conciseness in code.

Related benchmarks:

How to reduce an object to a sub-object fast (version: 0)

Comparing performance of: selectReduceAssign vs selectReduceSpread vs selectReduceAddExplicitly vs selectPick

Created: one year ago by: Registered User

Jump to the latest result

selectReduceAssign

selectReduceSpread

selectReduceAddExplicitly

selectPick

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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