Benchmark: new Date(date) vs new Date(normalizeToLocalDate(date))

Script Preparation code:

var dateTimeISO = '2024-08-21T17:00:00.000Z'
var dateOnlyISO = '2024-08-21'

var normalizeToLocalDate = (date) =>
    /^\s*\d{4}-\d{2}-\d{2}\s*$/.test(date) ? date.replace(/-/g, '/') : date;

Tests:

new Date(dateTimeISO)
new Date(dateTimeISO)
new Date(normalizeToLocalDate(dateTimeISO))
new Date(normalizeToLocalDate(dateTimeISO))
new Date(dateOnlyISO)
new Date(dateOnlyISO)
new Date(normalizeToLocalDate(dateOnlyISO))
new Date(normalizeToLocalDate(dateOnlyISO))

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
new Date(dateTimeISO)
new Date(normalizeToLocalDate(dateTimeISO))
new Date(dateOnlyISO)
new Date(normalizeToLocalDate(dateOnlyISO))

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36

Browser/OS: Chrome 127 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
new Date(dateTimeISO)	4275112.0 Ops/sec
new Date(normalizeToLocalDate(dateTimeISO))	3377427.8 Ops/sec
new Date(dateOnlyISO)	5799811.5 Ops/sec
new Date(normalizeToLocalDate(dateOnlyISO))	2309164.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark measures the performance of creating a new `Date` object using three different approaches:

1. **Simple ISO date string**: `new Date(dateTimeISO)`
2. **Normalized local date string**: `new Date(normalizeToLocalDate(dateTimeISO))`
3. **Date only ISO string**: `new Date(dateOnlyISO)`

Here, `dateTimeISO` and `dateOnlyISO` are predefined strings representing an ISO-formatted date in UTC (e.g., "2024-08-21T17:00:00.000Z" or just "2024-08-21").

**Normalized Local Date String**

The `normalizeToLocalDate` function takes a date string as input and returns the same string with any trailing whitespace removed, followed by an explicit slash (`/`) separator to make it suitable for local date parsing.

**Pros and Cons of Approaches:**

1. **Simple ISO Date String**: This approach is straightforward but may not handle edge cases (e.g., dates without a timezone). Modern browsers might also parse this string directly without invoking `Date`.
	* Pros: Simple, efficient.
	* Cons: May not handle all date formats or edge cases.
2. **Normalized Local Date String**: Using the `normalizeToLocalDate` function ensures that the input string is correctly formatted for local date parsing, which can help avoid errors and inconsistencies.
	* Pros: Handles edge cases, ensures correct formatting for local dates.
	* Cons: Adds an additional step (function call) before creating the `Date` object.
3. **Date Only ISO String**: This approach is more robust than the first one but still relies on the browser's ability to parse a specific date format.
	* Pros: Robust, handles most date formats without relying on browser-specific behavior.
	* Cons: Requires knowledge of a specific date format (ISO 8601).

**Library and Special JS Feature**

In this benchmark, no third-party libraries or special JavaScript features are used. The `normalizeToLocalDate` function is defined inline in the script preparation code.

**Other Considerations**

When creating a new `Date` object, consider factors like:

* Timezone: Some browsers (like Chrome) may parse dates without a timezone and assume UTC by default. Using a specific date format or handling timezone differences can be important depending on your use case.
* Browser behavior: Different browsers might behave differently when parsing dates, so testing across multiple browsers is essential.

**Alternative Approaches**

Other ways to create `Date` objects include:

* Using the `Date.parse()` method (which returns the number of milliseconds since the Unix epoch) and then creating a new `Date` object from that value.
* Utilizing libraries like Moment.js or Luxon, which provide more robust date handling and formatting capabilities.

These alternatives might be suitable for specific use cases but may not provide identical results to the original benchmark.

Related benchmarks:

new Date(date) vs new Date(normalizeToLocalDate(date)) (version: 0)

Comparing performance of: new Date(dateTimeISO) vs new Date(normalizeToLocalDate(dateTimeISO)) vs new Date(dateOnlyISO) vs new Date(normalizeToLocalDate(dateOnlyISO))

Created: 4 months ago by: Registered User

Jump to the latest result

new Date(dateTimeISO)

new Date(normalizeToLocalDate(dateTimeISO))

new Date(dateOnlyISO)

new Date(normalizeToLocalDate(dateOnlyISO))

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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