Javascript Regex: How to find index of each subexpression?

Question

Suppose I have the string: BLAH BLAH BLAH copy 2. I want to find the index of the two pieces, the word 'copy' and a number that may follow the word copy.

I have the regex: /(copy)\s+([0-9]+)$/i which successfully matches copy and 2 from the above string. How can I find the index of the number 2? I know I can use .index to find the position of the matched test 'copy 2', but I would like to get the position of '2' so that I can increment it.

Ωmega · Answer 1 · 2012-07-19T20:22:37.123

1

You should go with regex /^(.*?copy\s+)(\d+)$/i and then length of $1 is a position of $2 (copy number).

Edit: Your test code is (fiddle):

var str = "BLAH BLAH BLAH copy 2";
var m = str.match(/^(.*?copy\s+)(\d+)$/i);
alert("Found '" + m[2] + "' at position " + m[1].length);

edited Jul 19 '12 at 20:22

answered Jul 19 '12 at 20:04

Ωmega

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Not always. \s+ means there could be 1 or more spaces. – Stephen Melvin Jul 19 '12 at 20:06
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No, you do not know how much whitespace there is. – PointedEars Jul 19 '12 at 20:06
Yes, it will work ***always***, regardless of how many whitespace characters are there :) – Ωmega Jul 19 '12 at 20:19
My comment was posted well before you updated your answer. Apropos, I see no good reason for inserting `.*?` here, which is not backwards- compatible, and the `^` anchor that also was not in the original expression. – PointedEars Jul 19 '12 at 20:21
@PointedEars - Well, `.*?` may be changed to `.*` if there is `$` (don't know if OP wants allow some extra text behind *copy N*), but how the hell you want to get index by length of `$1` without `^`..? Teach me! – Ωmega Jul 19 '12 at 20:29
The update history does not have the wrong answer that says the number index was just `.index + 4`. It might have been by someone else. But Steve saw it, too. – PointedEars Jul 19 '12 at 20:29
@PointedEars - Not mine, boy... (you should clean up your irrelevant comments then) – Ωmega Jul 19 '12 at 20:30
You want to watch your manners. As for the index, if you replace `^(.*?` with `(`, it will still work if you add `m.index` as I suggested in my answer. – PointedEars Jul 19 '12 at 20:33

PointedEars · Answer 2 · 2012-07-19T20:19:55.690

1

If you modify the regular expression slightly, the index of the number can be computed:

var matches = "BLAH BLAH BLAH copy 2".match(/(copy)(\s+)([0-9]+)$/i);
var numberIndex = matches.index + matches[1].length + matches[2].length;

But you really do not need that in order to increment the number:

var matches = "BLAH BLAH BLAH copy 2".match(/(copy)\s+([0-9]+)$/i);
var incremented = (+matches[2]) + 1;

edited Jul 19 '12 at 20:19

answered Jul 19 '12 at 20:08

PointedEars

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score 1 · Accepted Answer · answered Jul 19 '12 at 20:11

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If you need to replace the copy number with an incremented number, use replace plus a replacer function:

'BLAH BLAH BLAH copy 2'.replace(/(copy )(\d+)/, function (s, s1, s2) {
    return s1 + (Number(s2) + 1);
});

answered Jul 19 '12 at 20:11

katspaugh

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score 0 · Answer 4 · answered Jul 19 '12 at 20:21

0

Change the regex /(copy)\s+([0-9]+)$/i to /^((.*)(copy)\s+)([0-9]+)$/i

Then the position of copy is the length of $2 and the position of the numbers is the length of $1. The number will be in $4

answered Jul 19 '12 at 20:21

Ed Heal

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Javascript Regex: How to find index of each subexpression?

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