Javascript Regex - Find all possible matches, even in already captured matches

Question

I\'m trying to obtain all possible matches from a string using regex with javascript. It appears that my method of doing this is not matching parts of the string

Answer 1

Unfortunately, it's not quite as simple as a single string.match.

The reason is that you want overlapping matches, which the /g flag doesn't give you.

You could use lookahead:

var re = /A\d+B\d+Y(?=:A\d+B\d+Y)/g;

But now you get:

string.match(re); // ["A1B1Y", "A1B2Y", "A1B5Y", "A1B6Y", "A1B9Y", "A1B10Y"]

The reason is that lookahead is zero-width, meaning that it just says whether the pattern comes after what you're trying to match or not; it doesn't include it in the match.

You could use exec to try and grab what you want. If a regex has the /g flag, you can run exec repeatedly to get all the matches:

// using re from above to get the overlapping matches

var m;
var matches = [];
var re2 = /A\d+B\d+Y:A\d+B\d+Y/g; // make another regex to get what we need

while ((m = re.exec(string)) !== null) {
  // m is a match object, which has the index of the current match
  matches.push(string.substring(m.index).match(re2)[0]);
}

matches == [
  "A1B1Y:A1B2Y", 
  "A1B2Y:A1B3Y", 
  "A1B5Y:A1B6Y", 
  "A1B6Y:A1B7Y", 
  "A1B9Y:A1B10Y", 
  "A1B10Y:A1B11Y"
];

Here's a fiddle of this in action. Open up the console to see the results

Alternatively, you could split the original string on :, then loop through the resulting array, pulling out the the ones that match when array[i] and array[i+1] both match like you want.