Question

I’m trying to make a simple Ruby regex to detect a JavaScript Declaration, but it fails.

Regex:

lines.each do |line|
     unminifiedvar = /var [0-9a-zA-Z] = [0-9];/.match(line)
     next if unminifiedvar == nil #no variable declarations on the line
     #...
end

Testing Line:

var testvariable10 = 9;

Answer 1

A variable name can have more than one character, so you need a + after the character-set [...]. (Also, JS variable names can contain other characters besides alphanumerics.) A numeric literal can have more than one character, so you want a + on the RHS too.

More importantly, though, there are lots of other bits of flexibility that you’ll find more painful to process with a regular expression. For instance, consider var x = 1+2+3; or var myString = "foo bar baz";. A variable declaration may span several lines. It need not end with a semicolon. It may have comments in the middle of it. And so on. Regular expressions are not really the right tool for this job.

Of course, it may happen that you’re parsing code from a particular source with a very special structure and can guarantee that every declaration has the particular form you’re looking for. In that case, go ahead, but if there’s any danger that the nature of the code you’re processing might change then you’re going to be facing a painful problem that really isn’t designed to be solved with regular expressions.

[EDITED about a day after writing, to fix a mistake kindly pointed out by “the Tin Man”.]