Benchmark: how fast is regex?

Script Preparation code:

const prepared = /[.*+?^${}()|[\]\\]/g;

Tests:

instantiate new regex
const blah = "whatever" const r = blah.replace(/[.*+?^${}()|[\]\\]/g, "\\$&")
use existing regex
const blah = "whatever" const r = blah.replace(prepared, "\\$&")

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
instantiate new regex
use existing regex

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:150.0) Gecko/20100101 Firefox/150.0

Browser/OS: Firefox 150 on Mac OS X 10.15

View result in a separate tab

Test name	Executions per second
instantiate new regex	35607608.0 Ops/sec
use existing regex	34647956.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

LLMs can make mistakes. Check important info.

The benchmark titled "how fast is regex?" compares the performance of two different approaches to using regular expressions in JavaScript: instantiating a new regular expression object each time versus using a pre-prepared regex object.

### Options Compared

1. **Instantiate New Regex**:
   - **Test Code**:  
     ```javascript
     const blah = "whatever";
     const r = blah.replace(/[.*+?^${}()|[\\]\\\\]/g, "\\$&");
     ```
   - **Description**: In this test, a new regular expression is created directly in the `replace()` function. Every time this line of code executes, a new regex object is instantiated.

2. **Use Existing Regex**:
   - **Test Code**:  
     ```javascript
     const blah = "whatever";
     const r = blah.replace(prepared, "\\$&");
     ```
   - **Description**: This test uses a regex that has been prepared beforehand (stored in the `prepared` variable). The regex is compiled only once and can be reused multiple times in the code.

### Pros and Cons

#### 1. Pros and Cons of Instantiating New Regex:
- **Pros**:
  - **Simplicity**: Writing regex inline can make the code easier to understand at first glance without needing separate variable declarations.
- **Cons**:
  - **Performance Overhead**: Each execution creates a new regex object. This can significantly slow down performance, especially when the regex operation is called repeatedly in loops or in performance-critical sections.

#### 2. Pros and Cons of Using Existing Regex:
- **Pros**:
  - **Performance**: Reusing an existing regex object eliminates the overhead of object instantiation, leading to faster execution times, as demonstrated by the benchmark results.
  - **Less Memory Usage**: Creating fewer objects can lead to lower memory consumption.
- **Cons**:
  - **Initial Complexity**: Requires more initial setup where the regex must be defined separately from where it is used.

### Benchmark Results

In the benchmark results, we can observe the following performance metrics:
- **"use existing regex"**: 14,546,399 executions per second.
- **"instantiate new regex"**: 14,238,132 executions per second.

The performance of the "use existing regex" approach is significantly better than that of instantiating a new regex, confirming the expectations around efficiency.

### General Considerations and Alternatives

- **Alternative Approaches**: While using pre-compiled regular expressions is generally more efficient, there are other ways to handle string transformations in JavaScript, such as using native string methods or other parsing libraries like `lodash` or `underscore.js`, which might offer specific functions targeting string manipulation or pattern matching more efficiently or with additional features.

- **Library Consideration**: In this benchmark, no external libraries are used, but libraries that help streamline regex operations (like validation libraries) may be beneficial for specific use cases, although they may also introduce additional overhead.

In conclusion, the benchmark decisively highlights that reusing regex objects can yield significant performance benefits in JavaScript compared to creating new instances each time, a vital consideration for optimizing string manipulation tasks in performance-sensitive contexts.

Related benchmarks:

how fast is regex? (version: 1)

Comparing performance of: instantiate new regex vs use existing regex

Created: one year ago by: Guest

Jump to the latest result

instantiate new regex

use existing regex

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):