Benchmark: prefix check - MeasureThat.net

Script Preparation code:

var prefixMap = new Map([['!', new RegExp('^!')]]);
var prefix = new RegExp('^!');
var message1 = '!test';
var message2 = 'test';

function startsWithPrefix (prefix, content) {
    for (let i = 0; i < prefix.length; i++)
        if (prefix[i] !== content[i]) return false;
    return true;
};

Tests:

startsWith
message1.startsWith('!'); message2.startsWith('!');
cached RegExp
prefix.test(message1); prefix.test(message2);
uncached RegExp
/^!/.test(message1); /^!/.test(message2);
prefixMap
prefixMap.get('!').test(message1); prefixMap.get('!').test(message2);
for function
startsWithPrefix('!', message1); startsWithPrefix('!', message2);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
startsWith
cached RegExp
uncached RegExp
prefixMap
for function

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

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Let's break down the benchmark and its various components.

**Benchmark Definition**

The provided JSON defines a JavaScript microbenchmark that tests different approaches for checking if a string starts with a specific prefix. The script preparation code creates a map (`prefixMap`) that stores regular expressions (regex) for certain prefixes, as well as two functions: `startsWithPrefix` and the built-in `RegExp.test`.

**Options Compared**

The benchmark compares the following options:

1. **Built-in `startsWith` method**: This is the standard JavaScript method for checking if a string starts with another string.
2. **`RegExp.test` without caching**: The regex pattern is created every time the test runs, without storing it in memory.
3. **Caching `RegExp` patterns using `prefixMap`**: A map (`prefixMap`) stores pre-created regex patterns for certain prefixes, reducing the overhead of creating a new regex on each test run.
4. **Using a custom function `startsWithPrefix`**: This function manually checks if the string starts with the prefix by iterating over the characters.

**Pros and Cons**

Here's a brief summary:

* **Built-in `startsWith` method**:
	+ Pros: Simple, widely supported, and well-optimized.
	+ Cons: May involve more overhead due to string manipulation.
* **`RegExp.test` without caching**:
	+ Pros: Fast and efficient when the regex pattern is not frequently used.
	+ Cons: Creates a new regex pattern on each test run, which can be slow.
* **Caching `RegExp` patterns using `prefixMap`**:
	+ Pros: Reduces overhead by storing pre-created regex patterns in memory.
	+ Cons: Requires more memory to store the map and its entries.
* **Using a custom function `startsWithPrefix`**:
	+ Pros: Allows for fine-grained control over the checking process.
	+ Cons: May be slower due to the manual iteration.

**Libraries Used**

There is no explicit library mentioned in the benchmark definition. However, `RegExp` is a built-in JavaScript object that provides regular expression matching capabilities.

**Special JS Features or Syntax**

The benchmark uses some advanced JavaScript features:

* **Map**: The `prefixMap` uses a Map data structure to store regex patterns.
* **Regular Expressions (regex)**: The benchmark creates and uses regex patterns to match the prefix.

**Other Considerations**

When writing performance benchmarks like this one, it's essential to consider factors such as:

* **Cache locality**: How well do the test cases cache their results? In this case, `prefixMap` caches its entries.
* **Memory allocation**: What is the impact of memory allocation on the benchmark's performance?
* **Garbage collection**: How does garbage collection affect the benchmark's execution time?

**Alternatives**

If you're interested in exploring alternative approaches for string prefix checking, consider:

* Using a different data structure, such as an array or object, to store regex patterns.
* Implementing a custom string matching algorithm that avoids using `RegExp`.
* Comparing performance with other languages or frameworks that provide optimized string manipulation capabilities.

Related benchmarks:

prefix check (version: 0)

Comparing performance of: startsWith vs cached RegExp vs uncached RegExp vs prefixMap vs for function

Created: 8 years ago by: Guest

Jump to the latest result

startsWith

cached RegExp

uncached RegExp

prefixMap

for function

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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