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My question is related to a previous Stackoverflow post, which says the following two ways have almost the same speed.
But when I test it actually using loop count 1000000, there seems to be a consistent performance. While I expect Example 1 should be faster, but it turns out to be slower than Example 2.
The results of the testing page are here. For example 1, the execution times are: [20.27,19.82, 16.17], but for example 2, they are less:[18.57, 15.48, 15.14].
The results confuse me a lot. Could anyone have a hint about the reason?
var str = "Hello World"; // Example 1 var regExp1 = /[aeiou]+/gi; for(var i = 0; i < 1000; ++i) regExp1.exec(str); // Example 2 for(var j = 0; j < 1000; ++j) /[aeiou]+/gi.exec(str);
It must be slower.
Because every time you go in a new iteration in the loop you re-evaluate the regex before executing it.
This causes a small delay but with large loops, there will be a time difference
In the 1st example, it is already defined and evaluated.
Hence, the only time needed is for the execution.
Regular expressions, Using a regular expression literal, which consists of a pattern enclosed for more information (but slower execution) use the exec() or match() methods. created with an object initializer without assigning it to a variable. In the example above, we used a literal RegEx /help/ to search for the word help in variable str1 and str2. Another example of literal RegEx can be /expect/ , which will match the word expect from
jsperf.com is showing ops/sec, not execution times. Thus the higher the value, the faster the code.
The first version is faster, not slower. You got confusing results by running different number of iterations in one test set. 20.27 ops/s is faster than 18.57 ops/s.
There is no question - caching the regexp in a separate variable is going to be faster than compiling it in each iteration (the V8 VM caches compiled regex'es but apparently not as efficiently as doing it explicitly).
Best Practices for Regular Expressions in .NET, Text that does not match the regular expression pattern. the slower execution speeds of interpreted regular expressions outweigh gains from� Best practices for regular expressions in .NET. 06/30/2020; 39 minutes to read +10; In this article. The regular expression engine in .NET is a powerful, full-featured tool that processes text based on pattern matches rather than on comparing and matching literal text. In most cases, it performs pattern matching rapidly and efficiently.
- How are you timing this? I think for the benchmark to be meaningful, it should only be measuring the calls to
exec(), and not anything else (the "anything else" not being relevant to the performance of the regex).
- The link that you've provided for conducting the tests measures Operations/sec and not time elapsed. When I ran the tests, I found that the ops/sec is more for Example 1 than Example 2 which means that method in Example 1 is actually faster than method in Example 2.