Unicode Escape and Unescape

Applications can Unicode escape and unescape text in a variety of styles and formats using the Chilkat API. See the following examples and explanations below.

Unicode Escape Formats

Chilkat supports the following types of Unicode escaping.

JSON-style (JavaScript-style) Unicode escape sequences

• \uXXXX
  • Represents a single 16-bit code unit in hexadecimal.
  • Originates from JavaScript string literal syntax and is also used in JSON.
  • Example: \u2705 = ✅ (White Heavy Check Mark).
• Surrogate pairs
  • Code points above U+FFFF (such as most emoji) are encoded as two \uXXXX sequences — a high surrogate (\uD800–\uDBFF) followed by a low surrogate (\uDC00–\uDFFF).
  • Example: \ud83e\udde0 → 🧠 (Brain).
    • \uD83E = high surrogate
    • \uDDE0 = low surrogate

Where you see it

• JSON data containing Unicode characters.
• JavaScript source strings.
• Many web APIs that serialize Unicode characters as escaped code units.

ECMAScript (JavaScript) “code point escape” syntax

Also called Unicode code point escapes.

• Written as \u{<hex>} instead of \uXXXX.
• Introduced in ES6 (ECMAScript 2015).
• Can directly represent:
  • Any Unicode code point from U+0000 to U+10FFFF.
  • Characters above U+FFFF without needing surrogate pairs.
• Example:
  • \u{1F9E0} → 🧠 (Brain)
  • \u{2705} → ✅ (White Heavy Check Mark)

Difference from the older \uXXXX form

• \uXXXX → always exactly 4 hex digits; represents a 16-bit UTF-16 code unit (may require two sequences for characters above U+FFFF).
• \u{...} → variable-length hex inside braces; represents a full Unicode code point directly.

Unicode code point notation or U+ notation

• Written as U+ (or lowercase u+) followed by the hexadecimal code point value.
  • Example: U+1F9E0 → 🧠 (Brain)
• Commonly used in:
  • Unicode charts and specifications.
  • Documentation and character tables.
  • Fonts and internationalization tools.
• It’s not a programming-language escape sequence — it’s a human-readable way to specify a Unicode character’s code point.
• Can list multiple code points for characters that are composed of more than one code point (e.g., U+26A0 U+FE0F = ️ warning sign with emoji presentation).

HTML hexadecimal character reference

Also known as an HTML numeric character reference in hexadecimal form.

• Syntax: &#x<hex>;
  • &# → starts a numeric reference
  • x → indicates hexadecimal
  • <hex> → the Unicode code point in hex
  • ; → terminates the reference
• Example:
  • 🧠 → 🧠 (Brain)
  • ✅ → ✅ (White Heavy Check Mark)
• Used in HTML and XML to represent characters that might otherwise cause encoding issues or be hard to type directly.
• Decimal form is also valid: 🛠 = 🧠.

HTML decimal character reference

or HTML numeric character reference in decimal form.

• Syntax: &#<decimal>;
  • &# → starts a numeric reference
  • <decimal> → the Unicode code point in decimal
  • ; → terminates the reference
• Example:
  • 🧠 → 🧠 (Brain)
  • ✅ → ✅ (White Heavy Check Mark)
• Decimal form is just the base-10 equivalent of the hexadecimal form (&#x...;).
• Works in HTML and XML for representing characters without directly embedding them.

Hex in Angle Brackets

This style isn’t a standard programming or HTML escape — it’s essentially a custom or ad-hoc code point notation where each Unicode code point is written in hexadecimal inside angle brackets.

• <1f9e0> is clearly intended to mean U+1F9E0 🧠(Brain).
• The values are plain hexadecimal Unicode code points.
• Angle brackets aren’t part of any official Unicode escape syntax — they’re just a delimiter someone chose (often used in internal documentation, markup, or proprietary text formats).
• It’s not HTML (<tag> syntax) — there’s no meaning assigned to these “tags” by browsers unless custom parsing code handles them.

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