Mathematical Double-Struck Capital J HTML entity &Jopf;

&Jopf; is the HTML entity for Mathematical Double-Struck Capital J 𝕁 (U+1D541). Copy 𝕁, 𝕁 and the CSS, JavaScript, Python and URL escapes.

Entity: &Jopf;
Code point: U+1D541
Unicode name: MATHEMATICAL DOUBLE-STRUCK CAPITAL J
Block: Mathematical Alphanumeric Symbols
Category: Uppercase letter (Lu)
Since: Unicode 3.1
Defined in: HTML5

Codes to copy

HTML named	`&Jopf;`Works in HTML; in XML only & < > " ' are predefined.
HTML decimal	`𝕁`Works in HTML and XML.
HTML hex	`𝕁`Works in HTML and XML.
CSS	`content: "\1D541";`In a stylesheet, for ::before and ::after.
JavaScript	`"\uD835\uDD41"`Also valid in JSON. Characters above U+FFFF are written as a surrogate pair.
JavaScript (ES6)	`"\u{1D541}"`Code point escape; not valid in JSON.
Python	`"\U0001d541"`Python 3 string literal.
Python by name	`"\N{MATHEMATICAL DOUBLE-STRUCK CAPITAL J}"`Readable alternative using the Unicode name.
URL	`%F0%9D%95%81`Percent-encoded UTF-8 bytes, for a path or query value.
UTF-8 bytes	`F0 9D 95 81`4 bytes.
UTF-16	`D835 DD41`2 code units, which is what JavaScript length counts.

When to use it

&Jopf; writes U+1D541 (Mathematical Double-Struck Capital J), a capital letter from the Unicode Mathematical Alphanumeric Symbols block, encoded since Unicode 3.1. These letters are distinct symbols in mathematics. Using them to style ordinary text breaks search, copy and screen readers.

The name comes from the HTML5 list (much of it shared with MathML), so it works in every current browser but not in XML or XHTML served as XML, where the numeric reference is the safe choice.

More maths letters: script, fraktur and double-struck

All maths letters: script, fraktur and double-struck · Every HTML entity · Encode or decode text

Source: the WHATWG HTML Standard list of named character references and the Unicode Character Database (Unicode 18.0).