Benchmark: Initializing array with n undefined items

Script Preparation code:

var n = 100000; // 100k

Tests:

[...Array(n).keys()].map(k => undefined)
[...Array(n).keys()].map(k => undefined);
Array.apply(null, { length: 4 })
Array.apply(null, { length: n });
Array.from
Array.from({ length: n }, () => undefined);
Array(n).fill(undefined)
Array(n).fill(undefined)
for loop push
const arr = []; for (let i = 0; i < n; i++) { arr.push(undefined); }

Historical Performance Data aggregated from 33 community runs

Desktop Results:

Chrome 24 runs

Array(n).fill(undefined)

4K/s

Array.apply(null, { length: 4 })

487/s

[...Array(n).keys()].map(k => undefined)

103/s

Array.from

94/s

for loop push

86/s

Fastest: Array(n).fill(undefined) (47.4x faster)

View exact numbers

✓ Array(n).fill(undefined): 4,074 ops/sec
• Array.apply(null, { length: 4 }): 487 ops/sec
• [...Array(n).keys()].map(k => undefined): 103 ops/sec
• Array.from: 94 ops/sec
• for loop push: 86 ops/sec

Firefox 9 runs

for loop push

3K/s

Array(n).fill(undefined)

2K/s

Array.from

1K/s

[...Array(n).keys()].map(k => undefined)

595/s

Array.apply(null, { length: 4 })

427/s

Fastest: for loop push (6.3x faster)

View exact numbers

✓ for loop push: 2,704 ops/sec
• Array(n).fill(undefined): 2,122 ops/sec
• Array.from: 1,037 ops/sec
• [...Array(n).keys()].map(k => undefined): 595 ops/sec
• Array.apply(null, { length: 4 }): 427 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
[...Array(n).keys()].map(k => undefined)
Array.apply(null, { length: 4 })
Array.from
Array(n).fill(undefined)
for loop push

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:148.0) Gecko/20100101 Firefox/148.0

Browser/OS: Firefox 148 on Linux

View result in a separate tab

Array(n).fill(undefined)

2K/s

for loop push

792/s

Array.from

720/s

[...Array(n).keys()].map(k => undefined)

349/s

Array.apply(null, { length: 4 })

269/s

View exact numbers

Test name	Executions per second
✓ Array(n).fill(undefined)	2,122 Ops/sec
for loop push	792 Ops/sec
Array.from	720 Ops/sec
[...Array(n).keys()].map(k => undefined)	349 Ops/sec
Array.apply(null, { length: 4 })	269 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark definition and explain what's being tested, compared, and their pros and cons.

**Benchmark Definition:**

The benchmark measures how fast JavaScript engines can initialize an array with `n` undefined items using different methods. The goal is to see which method is the fastest.

**Methods Compared:**

1. **Spread Operator**: `[...Array(n).keys()].map(k => undefined)`
2. **Array.prototype.apply()**: `Array.apply(null, { length: n })`
3. **Array.from()**: `Array.from({ length: n }, () => undefined)`
4. **Array.prototype.fill()**: `Array(n).fill(undefined)`
5. **For loop with push()**: `const arr = []; for (let i = 0; i < n; i++) { arr.push(undefined); }`

**Pros and Cons of Each Approach:**

1. **Spread Operator**:
	* Pros: Efficient, concise syntax.
	* Cons: May not be as optimized by modern engines.
2. **Array.prototype.apply()**:
	* Pros: Can be more efficient than the spread operator due to its ability to optimize array creation.
	* Cons: Less intuitive and verbose syntax.
3. **Array.from()**:
	* Pros: Newer method introduced in ES6, potentially optimized by modern engines.
	* Cons: May not be as widely supported or understood.
4. **Array.prototype.fill()**:
	* Pros: Efficient for large arrays, as it can fill the array with a single operation.
	* Cons: May not work correctly if `n` is not a power of 2.
5. **For loop with push()**:
	* Pros: Simple, intuitive syntax.
	* Cons: Generally slower than other methods due to the overhead of the loop.

**Library Used:**

None explicitly mentioned in the benchmark definition. However, some modern JavaScript engines might use optimized internal arrays or data structures that are not visible through the public API.

**Special JS Features or Syntax:**

The spread operator (`[...Array(n).keys()].map(k => undefined)`) is a relatively new feature introduced in ECMAScript 2015 (ES6). It's designed to provide a concise way to create arrays from iterables. While it's not a special syntax, it's an optimization technique that can be used in various contexts.

**Other Alternatives:**

If you need to initialize an array with undefined items, other alternatives might include:

* Using `Array(n).map(() => undefined)` or `Array(n).fill(undefined)`
* Creating an array from a generator function or an iterable
* Utilizing WebAssembly or other low-level optimizations (not recommended for most use cases)

Keep in mind that the choice of method ultimately depends on your specific requirements, performance needs, and personal preference.

Initializing array with n undefined items (version: 0)

worth to note that the maximum callstack size is exceeded for the first test case (spread operator) with n = 1 million

Comparing performance of: `[...Array(n).keys()].map(k => undefined) vs Array.apply(null, { length: 4 }) vs Array.from vs Array(n).fill(undefined) vs for loop push`

Created: 5 years ago by: Guest

Go to the latest result

[...Array(n).keys()].map(k => undefined)

Array.apply(null, { length: 4 })

Array.from

Array(n).fill(undefined)

for loop push

Historical Performance Data aggregated from 33 community runs

Desktop Results:

Chrome 24 runs

Firefox 9 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Initializing array with n undefined items (version: 0)

worth to note that the maximum callstack size is exceeded for the first test case (spread operator) with n = 1 million

Comparing performance of: [...Array(n).keys()].map(k => undefined) vs Array.apply(null, { length: 4 }) vs Array.from vs Array(n).fill(undefined) vs for loop push

Created: 5 years ago by: Guest

Go to the latest result

[...Array(n).keys()].map(k => undefined)

Array.apply(null, { length: 4 })

Array.from

Array(n).fill(undefined)

for loop push

Historical Performance Data aggregated from 33 community runs

Desktop Results:

Chrome 24 runs

Firefox 9 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

Comparing performance of: `[...Array(n).keys()].map(k => undefined) vs Array.apply(null, { length: 4 }) vs Array.from vs Array(n).fill(undefined) vs for loop push`