JavaScript RegExp \f Metacharacter

What You’ll Learn

The \f metacharacter matches a form feed (FF) control character—an invisible code historically used for page breaks on printers. Modern web apps rarely create form feeds, but regex helps you detect and clean them in legacy files and exports.

Introduction

Control characters are invisible codes embedded in strings. You already know \n for new lines and \r for carriage return. Form feed (\f) is another—it once told printers to start a new page.

You will not see form feeds in everyday user input, but they can appear in old documents, mainframe exports, and some PDF-to-text conversions. Regex lets you find and normalize them.

Understanding the \f Metacharacter

\f matches exactly one form feed character. Like other control codes, it is not visible when rendered but occupies one position in the string.

const text = "page1\fpage2";

/\f/.test(text);        // true
/\f/.test("hello");     // false

text.split("\f");       // ["page1", "page2"]

Form feed is also matched by the whitespace shorthand \s, which covers space, tab, newline, carriage return, form feed, and related separators.

How to Use \f in JavaScript

Typical tasks include detecting form feeds, splitting sections, and replacing them with newlines for display:

const raw = "Intro\fChapter 1\fChapter 2";

raw.match(/\f/g);              // ["\f", "\f"]
raw.split(/\f/);               // ["Intro", "Chapter 1", "Chapter 2"]
raw.replace(/\f/g, "\n\n");    // readable paragraphs

Use test() to check for presence, match() to count breaks, and replace() to convert form feeds into display-friendly spacing.

📝 Syntax

/\f/              // single form feed
/\f+/             // one or more form feeds
/\f/g             // all form feeds (global)
/\s/              // any whitespace (includes \f)
/[\f\n\r]+/       // form feed or line breaks

Common patterns

• /\f/g — find every form feed in a document.
• str.split(/\f/) — split into page-like sections.
• str.replace(/\f/g, "\n") — normalize to newlines.
• /[^\f]+/g — match text runs between form feeds.

Examples Gallery

Open DevTools Console (F12) or use Try-it links. Examples cover detection, splitting, replacement, whitespace classes, and cleanup.

const withFF = "section\fnext";
const plain = "section next";

console.log(/\f/.test(withFF));  // true
console.log(/\f/.test(plain));   // false
console.log(/\n/.test(withFF));  // false

true
false
false

const doc = "Title\fChapter 1\fChapter 2\fIndex";

const sections = doc.split(/\f/);
console.log(sections);
// ["Title", "Chapter 1", "Chapter 2", "Index"]

console.log(sections.length); // 4

["Title", "Chapter 1", "Chapter 2", "Index"]
4

const legacy = "Page A\fPage B\fPage C";

const readable = legacy.replace(/\f/g, "\n\n");
console.log(JSON.stringify(readable));
// "Page A\n\nPage B\n\nPage C"

"Page A\n\nPage B\n\nPage C"

const mixed = "a\f b\tc";

console.log(/\s/.test(mixed));           // true
console.log(mixed.match(/\s/g));        // ["\f", " ", "\t"]

console.log(/\f/.test(mixed));          // true
console.log(mixed.replace(/\s/g, "-")); // "a-b-c"

true
["\f", " ", "\t"]
true
a-b-c

const imported = "Report\fSummary\f2026";

const cleaned = imported.replace(/\f/g, " ");
console.log(cleaned);              // "Report Summary 2026"
console.log(/\f/.test(cleaned));   // false

Report Summary 2026
false

🚀 Common Use Cases

• Legacy file import — detect form feeds in old text exports.
• Document normalization — convert page breaks to newlines for HTML display.
• Section parsing — split reports into chapters or pages.
• Search indexing — strip control chars before tokenizing.
• Data validation — flag unexpected control characters in uploads.
• Whitespace cleanup — combine with \s for full whitespace normalization.

Important Considerations

• Invisible character — form feed does not show in normal UI; use JSON.stringify to debug.
• Not a newline — browsers may not render \f as a visible line break without replacement.
• Included in \s — broad whitespace patterns will match form feed even if you only wanted spaces.
• Rare in modern data — most web text uses \n; expect \f mainly in legacy sources.
• String escaping — in new RegExp() strings, write "\\f" for the regex escape.

📝 Notes

• \f is form feed; \n is line feed; they serve different purposes.
• Form feed is part of the \s whitespace set in JavaScript regex.
• Review \r carriage return and upcoming \n newline.
• Char code 12 identifies form feed: "\f".charCodeAt(0) === 12.
• For general whitespace cleanup, /\s+/g also removes form feeds.
• Modern apps rarely emit \f; treat it as a legacy-format signal.

💡 Best Practices