/
([\d]{4})([\d]{2})([\d]{2})([\d]{2})([\d]{2})([\d]{2})
/
gm
1st Capturing Group ([\d]{4})
Match a single character present in the list below [\d]{4}
{4} Quantifier — Matches exactly 4 times
\d matches a digit (equal to [0-9])
2nd Capturing Group ([\d]{2})
Match a single character present in the list below [\d]{2}
{2} Quantifier — Matches exactly 2 times
\d matches a digit (equal to [0-9])
3rd Capturing Group ([\d]{2})
Match a single character present in the list below [\d]{2}
{2} Quantifier — Matches exactly 2 times
\d matches a digit (equal to [0-9])
4th Capturing Group ([\d]{2})
Match a single character present in the list below [\d]{2}
{2} Quantifier — Matches exactly 2 times
\d matches a digit (equal to [0-9])
5th Capturing Group ([\d]{2})
Match a single character present in the list below [\d]{2}
{2} Quantifier — Matches exactly 2 times
\d matches a digit (equal to [0-9])
6th Capturing Group ([\d]{2})
Match a single character present in the list below [\d]{2}
{2} Quantifier — Matches exactly 2 times
\d matches a digit (equal to [0-9])
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Match 1
Full match  0-14    `20181008163451`
Group 1.    n/a `2018`
Group 2.    n/a `10`
Group 3.    n/a `08`
Group 4.    n/a `16`
Group 5.    n/a `34`
Group 6.    n/a `51`

number

([\d]{4})([\d]{2})([\d]{2})([\d]{2})([\d]{2})([\d]{2})
([\d]{4})([\d]{2})([\d]{2})([\d]{2})([\d]{2})([\d]{2})

20181008163451
const regex = /([\d]{4})([\d]{2})([\d]{2})([\d]{2})([\d]{2})([\d]{2})/gm;
const str = `20181008163451`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }

    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}