Is there any way to embed a ment in a JavaScript regex, like you can do in Perl? I'm guessing there is not, but my searching didn't find anything stating you can or can't.
Is there any way to embed a ment in a JavaScript regex, like you can do in Perl? I'm guessing there is not, but my searching didn't find anything stating you can or can't.
Share Improve this question edited May 23, 2017 at 11:51 CommunityBot 11 silver badge asked Nov 8, 2013 at 17:28 xdhmoorexdhmoore 9,93512 gold badges54 silver badges99 bronze badges2 Answers
Reset to default 14You can't embed a ment in a regex literal.
You may insert ments in a string construction that you pass to the RegExp constructor :
var r = new RegExp(
"\\b" + // word boundary
"A=" + // A=
"(\\d+)"+ // what is captured : some digits
"\\b" // word boundary again
, 'i'); // case insensitive
But a regex literal is so much more convenient (notice how I had to escape the \
) I'd rather separate the regex from the ments : just put some ments before your regex, not inside.
EDIT 2018: This question and answer are very old. EcmaScript now offers new ways to handle this, and more precisely template strings.
For example I now use this simple utility in node:
module.exports = function(tmpl){
let [, source, flags] = tmpl.raw.toString()
.replace(/\s*(\/\/.*)?$\s*/gm, "") // remove ments and spaces at both ends of lines
.match(/^\/?(.*?)(?:\/(\w+))?$/); // extracts source and flags
return new RegExp(source, flags);
}
which lets me do things like this or this or this:
const regex = rex`
^ // start of string
[a-z]+ // some letters
bla(\d+)
$ // end
/ig`;
console.log(regex); // /^[a-z]+bla(\d+)$/ig
console.log("Totobla58".match(regex)); // [ 'Totobla58' ]
Now with the grave backticky things, you can do inline ments with a little finagling. Note that in the example below there are some assumptions being made about what won't appear in the strings being matched, especially regarding the whitespace. But I think often you can make intentional assumptions like that, if you write the process()
function carefully. If not, there are probably creative ways to define the little "mini-language extension" to regexes in such a way as to make it work.
function process() {
var regex = new RegExp("\\s*([^#]*?)\\s*#.*$", "mg");
var output = "";
while ((result = regex.exec(arguments[0])) !== null ){
output += result[1];
}
return output;
}
var a = new RegExp(process `
^f # matches the first letter f
.* # matches stuff in the middle
h # matches the letter 'h'
`);
console.log(a);
console.log(a.test("fish"));
console.log(a.test("frog"));
Here's a codepen.
Also, to the OP, just because I feel a need to say this, this is neato, but if your resulting code turns out just as verbose as the string concatenation or if it takes you 6 hours to figure out the right regexes and you are the only one on your team who will bother to use it, maybe there are better uses of your time...
I hope you know that I am only this blunt with you because I value our friendship.