Unnecessary Regular Expressions

Regular expressions are powerful. They are the jackhammer for all chiseling purposes. In some situations they work great, but often they are either overkill or computationally unreasonable.

Regular expressions introduce a state-machine that is hard to optimize for each case.

Here are a couple regular expressions that I’ve seen within code that was replaced with easier-to-read and faster code.

s.replace(/[^.]*/g, “”).length

This regular expression removes all non-period characters in a string. It then queries for the length of the new string. This effectively just gets the number of periods in the string.

A much simpler approach, and also faster, would be to walk through the string and just count each instance of the period character.

var i, l = s.length, count = 0;
for (i = 0; i < l; i++) {
  if (s[i] == '.')
    count++;
}

s.replace(/\s+$/, “”)

This regular expression removes all whitespace at the end of the string. A much simpler approach would be to use the trim() function. There also exists non-standard functions trimRight() and trimLeft() that can be used to only remove whitespace from a specified side of the string.

Testing it out

If you’d like to see the performance differences for yourself, you can run the character counting and string trimming benchmarks on JSPerf.