JavaScript RegExp d Flag

What Is the d Flag?

The d flag (also called hasIndices) adds an indices property to match results. Each entry is a [start, end) range for the full match and every capture group—same half-open style as String.slice.

/pattern/d          // enable indices
regex.hasIndices    // true when d is set

match.indices[0]    // [start, end) full match
match.indices[1]    // [start, end) group 1
match.indices.groups // named group ranges

d flag ≠ \d digit metacharacter

How to Use the d Flag

Add d, run a match, then read indices (or indices.groups).

1. Create a regex with the flag: /pattern/d or new RegExp("pattern", "d").
2. Call exec, match, or (with g) matchAll.
3. Read match.indices[n] for the full match (0) and each group.
4. Use text.slice(start, end) to pull substrings or wrap them in markup.

Pseudocode

re = /pattern/d
m = re.exec(text)

if m is null:
    no match

else:
    m[0], m[1], …           // matched text
    m.indices[0] = [s0, e0] // full match range
    m.indices[1] = [s1, e1] // group 1 range (or undefined)

    text.slice(s0, e0) === m[0]

Cheat Sheet

Keep these facts handy when working with match positions.

Live Preview

Run a pattern with the d flag against "Code: AB-12 done" and inspect indices.

text = "Code: AB-12 done"
/([A-Z]+)-(\d+)/d.exec(text)

m[0] = "AB-12"
indices[0] = [6, 11]
indices[1] = [6, 8]   → "AB"
indices[2] = [9, 11]  → "12"

JavaScript Examples

Short, copy-ready snippets. Open DevTools Console, or use Try It Yourself for a live editor.

const text = "Code: AB-12 done";
const re = /([A-Z]+)-(\d+)/d;
const m = re.exec(text);

console.log(m[0]);           // "AB-12"
console.log(m.indices[0]);   // [6, 11]
console.log(m.indices[1]);   // [6, 8]  → "AB"
console.log(m.indices[2]);   // [9, 11] → "12"
console.log(re.hasIndices);  // true

AB-12
[ 6, 11 ]
[ 6, 8 ]
[ 9, 11 ]
true

function highlight(text, re) {
  const m = re.exec(text);
  if (!m?.indices) return text;
  const [start, end] = m.indices[0];
  return text.slice(0, start) + "[" + text.slice(start, end) + "]" + text.slice(end);
}

console.log(highlight("Find the word hello here", /hello/d));
// "Find the word [hello] here"

Find the word [hello] here

const re = /(?<year>\d{4})-(?<month>\d{2})/d;
const m = re.exec("Event on 2026-07-17");

console.log(m.groups.year);                 // "2026"
console.log(m.indices.groups.year);         // [9, 13]
console.log(m.groups.month);                // "07"
console.log(m.indices.groups.month);        // [14, 16]

2026
[ 9, 13 ]
07
[ 14, 16 ]

Performance Notes

Recording indices is cheap compared with matching itself. Prefer d over re-searching the string for each capture when you need offsets.

Key Takeaways