Benchmark: startsWith() vs always replace()

Tests:

Using replace
var n = 0; while(true) { var authHeader = 'asdf123asdf123asdf123asdf123asdf123asdf123'; authHeader.replace('Bearer ', ''); n++; if(n==100000) break; }
Using startsWith
var n = 0; while(true) { var authHeader = 'asdf123asdf123asdf123asdf123asdf123asdf123'; if (authHeader.startsWith('Bearer ')) authHeader.slice('Bearer '.length); n++; if(n==100000) break; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Using replace
Using startsWith

Fastest: N/A

Slowest: N/A

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 and explain what's being tested, compared, and some pros and cons of different approaches.

**Benchmark Definition**

The benchmark is designed to compare two approaches: `replace()` and `startsWith()`. The goal is to measure which approach is faster for a specific task: removing a prefix from a string (`"Bearer "`).

**Test Cases**

There are two test cases:

1. **Using replace**: This test case creates an infinite loop where it repeatedly removes the prefix `"Bearer "` from a fixed string `authHeader`. The loop breaks after 100,000 iterations.
2. **Using startsWith**: This test case also creates an infinite loop but uses the `startsWith()` method to check if the string `authHeader` starts with `"Bearer "` before removing it.

**Library and its Purpose**

In both test cases, the `slice()` function is used to remove the prefix from the string. The `slice()` function is a built-in JavaScript method that returns a new string by extracting a section of the original string. In this case, it's used to remove the first 7 characters (`"Bearer "`).

**Special JS Feature/Syntax**

Neither test case uses any special JavaScript features or syntax beyond what's commonly available in modern JavaScript engines.

**Other Considerations**

When measuring performance differences between `replace()` and `startsWith()`, we should consider factors like:

* String creation: How much overhead does creating a new string have compared to modifying an existing one?
* Method invocation: Are there any difference in method call performance or caching between the two approaches?
* Loop optimization: Will the engine optimize the loop for either approach, potentially affecting performance?

**Pros and Cons of Different Approaches**

Here's a brief summary:

* **Using replace()**:
	+ Pros: Can be faster because it only modifies the original string, reducing object creation.
	+ Cons: May require more CPU cycles to perform the replacement, especially if the replacement involves more complex logic.
* **Using startsWith()**:
	+ Pros: Can be faster if the engine can cache the result of the `startsWith()` call or optimize the loop for this specific use case.
	+ Cons: Requires creating a new string using `slice()`, which may incur additional overhead.

**Alternatives**

Other alternatives to consider when measuring performance differences between string manipulation methods:

* Using regular expressions (`RegExp`)
* Using `indexOf()` and `substring()` instead of `startsWith()` and `slice()`
* Using a different approach, like using a custom implementation for the prefix removal logic

Keep in mind that the specific use case and requirements might influence the choice of alternative approaches.

**Benchmark Result Interpretation**

The provided benchmark results show that Chrome 120 performed better with the `startsWith()` method (2717.4013671875 executions per second) compared to the `replace()` method (304.0390319824219 executions per second). This suggests that, for this specific use case and implementation, `startsWith()` might be faster due to potential optimizations or caching.

However, it's essential to note that these results are specific to this particular benchmark and might not generalize across all scenarios or implementations.

Latest run results:

Run details: (Test run date: 10 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Browser/OS: Chrome 120 on Windows

View result in a separate tab

Test name	Executions per second
Using replace	304.0 Ops/sec
Using startsWith	2717.4 Ops/sec

Related benchmarks:

startsWith() vs always replace() (version: 0)

This benchmark compares always doing a replace() vs checking if string starts with

Comparing performance of: Using replace vs Using startsWith

Created: 10 months ago by: Guest

Jump to the latest result

Using replace

Using startsWith

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):