How can I match overlapping strings with regex?

Question

Let\'s say I have the string

\"12345\"

If I .match(/\\d{3}/g), I only get one match, \"123\". Why don\'t I get

Answer 1

To answer the "How", you can manually change the index of the last match (requires a loop) :

var input = '12345', 
    re = /\d{3}/g, 
    r = [], 
    m;
while (m = re.exec(input)) {
    re.lastIndex -= m[0].length - 1;
    r.push(m[0]);
}
r; // ["123", "234", "345"]

Here is a function for convenience :

function matchOverlap(input, re) {
    var r = [], m;
    // prevent infinite loops
    if (!re.global) re = new RegExp(
        re.source, (re+'').split('/').pop() + 'g'
    );
    while (m = re.exec(input)) {
        re.lastIndex -= m[0].length - 1;
        r.push(m[0]);
    }
    return r;
}

Usage examples :

matchOverlap('12345', /\D{3}/)      // []
matchOverlap('12345', /\d{3}/)      // ["123", "234", "345"]
matchOverlap('12345', /\d{3}/g)     // ["123", "234", "345"]
matchOverlap('1234 5678', /\d{3}/)  // ["123", "234", "567", "678"]
matchOverlap('LOLOL', /lol/)        // []
matchOverlap('LOLOL', /lol/i)       // ["LOL", "LOL"]