JavaScript RegExp Null Character Metacharacter (\0)

What Is \0?

\0 matches the null character (NUL, U+0000, code point 0). It is invisible in normal text and often used as a separator or terminator in legacy / binary-oriented data.

\0     → null character (U+0000)
\x00   → same null (hex form — safer near digits)
\u0000 → same null (Unicode form in strings/patterns)

/\0/.test("hello")         → false
/\0/.test("hello\u0000")   → true
"a\u0000b".replace(/\x00/g, "") → "ab"

How to Use \0

Treat NUL as a real character you can test for, split on, or strip out.

1. Create fixtures with "\u0000" or String.fromCharCode(0).
2. Use /\0/ or /\x00/ with test, split, or replace.
3. Add the g flag when every null byte must be removed.
4. Prefer \x00 if the next pattern character might be a digit.

Pseudocode

pattern has "\0" (or "\x00")
read next character ch from the string

if ch.codePoint === 0:   // NUL
    accept match
else:
    fail this path

common actions:
  test(str)              → true if any NUL exists
  split(str)             → parts between NULs
  replace(/\x00/g, "")   → strip every NUL

Cheat Sheet

Keep these facts handy when sanitizing null bytes.

Live Preview

Run common \0 operations on sample strings that contain a null byte.

text = "hello"
/\0/.test(text)
→ false

/* no null character present */

JavaScript Examples

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

console.log(/\0/.test("hello"));       // false
console.log(/\0/.test("hello\u0000")); // true
console.log(/\0/.test("a\u0000b"));    // true

false
true
true

const dirty = "user\u0000name\u0000";

const clean = dirty.replace(/\x00/g, "");
console.log(clean);        // "username"
console.log(clean.length); // 8

username
8

const sample = "x\u0000y";

console.log(/\0/.test(sample));   // true
console.log(/\x00/.test(sample)); // true
console.log(sample.charCodeAt(1)); // 0

true
true
0

Performance Notes

Matching a single control character is cheap. Prefer an explicit \x00 strip when cleaning untrusted text; do not assume \s will remove NUL.

Key Takeaways