The benchmark titled "RegExp constructor vs literal + instantiation" is designed to evaluate the performance differences between using a RegExp constructor (new RegExp) and a regular expression literal (defined with slashes /.../) when testing patterns against input strings in JavaScript. The test specifically checks the execution speed of both approaches for running regular expression tests.
Test Cases
Test Case: new RegExp('^[0-9a-fA-F]{24}$').test('132abc67219f019afe12901a')
- Test Name: "new RegExp()"
- This test creates a new instance of a regular expression object using the constructor
new RegExp(). It evaluates whether the input string '132abc67219f019afe12901a' matches the pattern defined—in this case, checking for a hexadecimal string of exactly 24 characters.
Test Case: /^[0-9a-fA-F]{24}$/.test('132abc67219f019afe12901a')
- Test Name: "Literal"
- This test applies a regular expression literal to check the same input against the same criteria as the previous test using a more concise syntax with a literal.
Performance Results
The benchmark results indicate:
- Literal Method: Approximately 14,857,931 executions per second.
- RegExp Constructor Method: Approximately 8,591,375 executions per second.
Pros and Cons of Each Approach
1. Regular Expression Literal
- Pros:
- Generally faster execution, as indicated by the benchmark results.
- Easier to read and write for most use cases, as it follows a more concise syntax.
- Compiled at parse time, which can lead to improved speed since the JavaScript engine can optimize it directly.
- Cons:
- Less flexible if you need to dynamically construct the pattern. You cannot use variables to form the regex easily.
2. RegExp Constructor
- Pros:
- Allows for dynamic creation of regex patterns using variables, making it easy to alter the expression at runtime.
- Useful in scenarios where the pattern requires runtime information, such as user input.
- Cons:
- Slower performance compared to literals.
- Requires the pattern to be provided as a string, which can be less readable and might need additional escape characters.
Other Considerations
- In typical scenarios where the pattern is static, favoring regex literals can improve performance.
- In cases requiring dynamic regex patterns, the constructor becomes a necessary choice despite the performance overhead.
- If you need to use patterns periodically, pre-compiling a regex with the constructor and reusing it can mitigate some performance drawbacks.
Alternatives
- String Matching: If exact string matches are needed without regex complexity, using simple string comparison methods like
String.includes(), String.startsWith(), or String.endsWith() might yield better performance.
- Third-Party Libraries: Libraries like XRegExp provide extended capabilities for regex that go beyond standard JavaScript regex features and may optimize performance in some specific complex use cases.
By understanding the differences between using a regex constructor and regex literals, engineers can make informed decisions tailored to their specific application requirements, balancing readability, performance, and flexibility.
