JavaScript RegExp \ooo Octal Escape

What Is \ooo?

\ooo is a legacy octal escape: a backslash plus one to three digits from 0–7. It matches the character at that code — for example \101 is A, and \012 is a newline.

\ooo     → character at octal value ooo

\101     → "A"   (octal 101 = dec 65)
\141     → "a"   (octal 141 = dec 97)
\012     → newline  (same as \n)
\011     → tab      (same as \t)

digits: 0–7 only
length: 1–3 digits (max \377 = 255)

How to Use \ooo

Write one to three octal digits after \, then test as usual — mainly when reading legacy code.

1. Convert the character code to octal (digits 0–7 only), up to three digits (max 377).
2. Put it in a pattern without the u/v flag — e.g. /\101/.
3. Call test, match, or split on your string.
4. For new code, rewrite to \xHH, \uXXXX, or a shorthand like \n.

Pseudocode

pattern contains "\" + ooo   // ooo = 1–3 digits, each 0–7

value = parse_octal(ooo)     // 0 … 255
target = character(value)

for each char in input:
    if char == target:
        match this position
    else:
        try next / fail

Cheat Sheet

Keep these octal facts handy when reading older patterns.

Live Preview

Pick an octal escape and see what character it matches (and its hex twin).

/\101/.test("ABC")
→ true

/* octal 101 = dec 65 = "A" (= \x41) */

JavaScript Examples

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

console.log(/\101/.test("A"));    // true
console.log(/\101/.test("B"));    // false
console.log(/\101/.test("ABC"));  // true
console.log(parseInt("101", 8));  // 65

true
false
true
65

const text = "line1\nline2";
const row = "name\tage";

console.log(/\012/.test(text));   // true
console.log(text.split(/\012/));  // ["line1", "line2"]
console.log(/\011/.test(row));    // true
console.log(row.split(/\011/));   // ["name", "age"]

true
[ 'line1', 'line2' ]
true
[ 'name', 'age' ]

const ch = "A";

console.log(/\101/.test(ch));   // true (octal)
console.log(/\x41/.test(ch));   // true (hex)
console.log(/\u0041/.test(ch)); // true (Unicode)

// Modern preference for the same character:
console.log(/\x41/.test(ch));   // prefer this in new code

true
true
true
true

Performance Notes

Octal escapes resolve at compile time to a single character — same match cost as \x41 or a literal A. Choose notation for clarity and Unicode-mode compatibility, not speed.

Key Takeaways